<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:04021d1a-6ffd-4fba-bbdf-166cd9bb7e47,g:556810b8-ee4a-4595-af6f-de4fe9bdf334-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://jrgh.net/role/CondensedConsolidatedBalanceSheetsParentheticals" xlink:type="simple" xlink:href="jrvr-20250331.xsd#CondensedConsolidatedBalanceSheetsParentheticals"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/CondensedConsolidatedBalanceSheetsParentheticals" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_4c0209c4-3b12-462a-91a3-f7d80fcbe506" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_StatementTable_4c0209c4-3b12-462a-91a3-f7d80fcbe506" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_729a91b8-7587-44d6-a6ea-d4847b0e44c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_4c0209c4-3b12-462a-91a3-f7d80fcbe506" xlink:to="loc_us-gaap_FinancialInstrumentAxis_729a91b8-7587-44d6-a6ea-d4847b0e44c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_729a91b8-7587-44d6-a6ea-d4847b0e44c3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_729a91b8-7587-44d6-a6ea-d4847b0e44c3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_729a91b8-7587-44d6-a6ea-d4847b0e44c3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b5578657-bb4c-4089-9c49-6da6080db2ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_729a91b8-7587-44d6-a6ea-d4847b0e44c3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b5578657-bb4c-4089-9c49-6da6080db2ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_991e289f-8d48-48bd-8791-5607ea0d726c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b5578657-bb4c-4089-9c49-6da6080db2ed" xlink:to="loc_us-gaap_DebtSecuritiesMember_991e289f-8d48-48bd-8791-5607ea0d726c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_b8b47441-a05b-447d-a41b-4e386d34f10c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_b8b47441-a05b-447d-a41b-4e386d34f10c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCost_2f8ba014-ef77-4c00-bc06-bf3b028fc13f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesFvNiCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCost_2f8ba014-ef77-4c00-bc06-bf3b028fc13f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_28e5d15d-81af-4e70-9a55-e326145bb970" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_28e5d15d-81af-4e70-9a55-e326145bb970" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_59a2cee6-4c2b-4c8e-9529-6b103f0b0b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_59a2cee6-4c2b-4c8e-9529-6b103f0b0b1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_3cf3579c-1c49-458c-9338-ac643ee8257f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_3cf3579c-1c49-458c-9338-ac643ee8257f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_2ad61a38-5ff7-4ae4-9aab-d6e078199d48" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_2ad61a38-5ff7-4ae4-9aab-d6e078199d48" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_d175edf7-e7bc-4a26-9b74-49628e1a17c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_d175edf7-e7bc-4a26-9b74-49628e1a17c5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_527cf2a5-0a56-4aa9-8476-549fbaf33499" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_CommonStockSharesIssued_527cf2a5-0a56-4aa9-8476-549fbaf33499" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_6ea192f7-fa21-4d4f-84ad-9ffc5a5185da" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_6ea192f7-fa21-4d4f-84ad-9ffc5a5185da" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_cdc875b6-9579-4077-a8f1-05b579775464" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_cdc875b6-9579-4077-a8f1-05b579775464" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_1c167940-a917-485e-8381-d7ae18adb7c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_1c167940-a917-485e-8381-d7ae18adb7c8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_04eec5ad-5022-4cbd-9c85-fe5363555d69" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_PreferredStockSharesIssued_04eec5ad-5022-4cbd-9c85-fe5363555d69" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_15f28582-2f5b-4da4-9ce2-dc85a5270b3e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_11a11520-5f0d-4997-82ba-6d4d508f60c8" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_15f28582-2f5b-4da4-9ce2-dc85a5270b3e" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CondensedConsolidatedStatementsofChangesinShareholdersEquityUnaudited" xlink:type="simple" xlink:href="jrvr-20250331.xsd#CondensedConsolidatedStatementsofChangesinShareholdersEquityUnaudited"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/CondensedConsolidatedStatementsofChangesinShareholdersEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_dfa7b9d7-d48e-40ce-b904-bab07e1d9573" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_9a515f4b-06a4-4240-88f3-937ff82fa7ef" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_dfa7b9d7-d48e-40ce-b904-bab07e1d9573" xlink:to="loc_us-gaap_StatementTable_9a515f4b-06a4-4240-88f3-937ff82fa7ef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_596103d9-21c7-4e19-aa50-ac9da2320340" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9a515f4b-06a4-4240-88f3-937ff82fa7ef" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_596103d9-21c7-4e19-aa50-ac9da2320340" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_596103d9-21c7-4e19-aa50-ac9da2320340_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_596103d9-21c7-4e19-aa50-ac9da2320340" xlink:to="loc_us-gaap_EquityComponentDomain_596103d9-21c7-4e19-aa50-ac9da2320340_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_9c29dd96-2bcb-4ad5-9a34-3382b5101147" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_596103d9-21c7-4e19-aa50-ac9da2320340" xlink:to="loc_us-gaap_EquityComponentDomain_9c29dd96-2bcb-4ad5-9a34-3382b5101147" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_182f9a48-4b8a-4b23-a079-e424efe134fb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c29dd96-2bcb-4ad5-9a34-3382b5101147" xlink:to="loc_us-gaap_CommonStockMember_182f9a48-4b8a-4b23-a079-e424efe134fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_f0327b96-3567-4263-8495-6c62ef0b071e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c29dd96-2bcb-4ad5-9a34-3382b5101147" xlink:to="loc_us-gaap_PreferredStockMember_f0327b96-3567-4263-8495-6c62ef0b071e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_379cbfc6-7f94-4ce1-939e-e53dee5d606e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c29dd96-2bcb-4ad5-9a34-3382b5101147" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_379cbfc6-7f94-4ce1-939e-e53dee5d606e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_021b63f0-5070-4d4b-9d77-374509bc19ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c29dd96-2bcb-4ad5-9a34-3382b5101147" xlink:to="loc_us-gaap_RetainedEarningsMember_021b63f0-5070-4d4b-9d77-374509bc19ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_6d1768a6-49fe-4cc8-a45f-06b162399c92" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c29dd96-2bcb-4ad5-9a34-3382b5101147" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_6d1768a6-49fe-4cc8-a45f-06b162399c92" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfa7b9d7-d48e-40ce-b904-bab07e1d9573" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_e7cb454b-49e7-429f-8ede-d2f5a5134a36" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_e7cb454b-49e7-429f-8ede-d2f5a5134a36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_9ef61a4a-2d3c-4d60-be44-2733422dabf1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_StockholdersEquity_9ef61a4a-2d3c-4d60-be44-2733422dabf1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_4e9c0b9a-ec1c-482e-b470-56c236bb594b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_NetIncomeLoss_4e9c0b9a-ec1c-482e-b470-56c236bb594b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_cf496dff-71bf-48cb-9fb4-4ed7f1f434f5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_cf496dff-71bf-48cb-9fb4-4ed7f1f434f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_f88b266f-b301-4e1f-ae90-64e0eddbb60d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_f88b266f-b301-4e1f-ae90-64e0eddbb60d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_215a114a-b249-428a-b6d4-b726cc850a1d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_215a114a-b249-428a-b6d4-b726cc850a1d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_b0082389-4188-45c1-b4d4-6a2753981ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_b0082389-4188-45c1-b4d4-6a2753981ae0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_72de72de-52d2-4d87-a557-7b07a3e5c713" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_DividendsPreferredStock_72de72de-52d2-4d87-a557-7b07a3e5c713" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_b8862eca-9689-48de-b217-71babed114ff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f7f89b22-30bb-42d3-8d9f-c546683e54ed" xlink:to="loc_us-gaap_DividendsCommonStock_b8862eca-9689-48de-b217-71babed114ff" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_3991f47f-82d1-4842-a283-48080b231bf2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b5a3aa45-38d0-4b5a-9576-0e1bcf297269" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/AccountingPoliciesDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#AccountingPoliciesDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/AccountingPoliciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AccountingPoliciesLineItems_25701f72-05bc-4428-8de3-9535fce4f503" xlink:href="jrvr-20250331.xsd#jrvr_AccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AccountingPoliciesTable_31c3ee89-c89b-4f08-afe2-1a3edbd882c5" xlink:href="jrvr-20250331.xsd#jrvr_AccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_AccountingPoliciesLineItems_25701f72-05bc-4428-8de3-9535fce4f503" xlink:to="loc_jrvr_AccountingPoliciesTable_31c3ee89-c89b-4f08-afe2-1a3edbd882c5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_a9089bcd-e164-4ab6-be9a-15007de32070" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_AccountingPoliciesTable_31c3ee89-c89b-4f08-afe2-1a3edbd882c5" xlink:to="loc_srt_StatementGeographicalAxis_a9089bcd-e164-4ab6-be9a-15007de32070" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_a9089bcd-e164-4ab6-be9a-15007de32070_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_a9089bcd-e164-4ab6-be9a-15007de32070" xlink:to="loc_srt_SegmentGeographicalDomain_a9089bcd-e164-4ab6-be9a-15007de32070_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_38e24a98-3480-4ad6-82c6-3431bf1008db" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_a9089bcd-e164-4ab6-be9a-15007de32070" xlink:to="loc_srt_SegmentGeographicalDomain_38e24a98-3480-4ad6-82c6-3431bf1008db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_f90ceafa-7823-43c7-9cb8-3a4ebf40658c" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_38e24a98-3480-4ad6-82c6-3431bf1008db" xlink:to="loc_country_US_f90ceafa-7823-43c7-9cb8-3a4ebf40658c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfInsuranceCompanies_a814c1a9-5f9b-4130-8824-5f251b327b5d" xlink:href="jrvr-20250331.xsd#jrvr_NumberOfInsuranceCompanies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AccountingPoliciesLineItems_25701f72-05bc-4428-8de3-9535fce4f503" xlink:to="loc_jrvr_NumberOfInsuranceCompanies_a814c1a9-5f9b-4130-8824-5f251b327b5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_c6523eea-0aa5-4c2c-847b-9c5349629862" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AccountingPoliciesLineItems_25701f72-05bc-4428-8de3-9535fce4f503" xlink:to="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_c6523eea-0aa5-4c2c-847b-9c5349629862" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_64b173f3-4d37-4d27-a63f-1da80f2bfa3c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AccountingPoliciesLineItems_25701f72-05bc-4428-8de3-9535fce4f503" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_64b173f3-4d37-4d27-a63f-1da80f2bfa3c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/DiscontinuedOperationsNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#DiscontinuedOperationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/DiscontinuedOperationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_276593b1-c176-47c2-b172-0ad63cfd7ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_276593b1-c176-47c2-b172-0ad63cfd7ea3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_e6bec2e8-9312-401c-a10b-151deb526fab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_276593b1-c176-47c2-b172-0ad63cfd7ea3" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_e6bec2e8-9312-401c-a10b-151deb526fab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_e6bec2e8-9312-401c-a10b-151deb526fab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_e6bec2e8-9312-401c-a10b-151deb526fab" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_e6bec2e8-9312-401c-a10b-151deb526fab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_046aa367-db6c-49b6-826e-82f5236d85ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_e6bec2e8-9312-401c-a10b-151deb526fab" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_046aa367-db6c-49b6-826e-82f5236d85ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_844fdd19-3f1d-488f-88f7-32f3c52747f0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_046aa367-db6c-49b6-826e-82f5236d85ed" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_844fdd19-3f1d-488f-88f7-32f3c52747f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_43180e2b-49dc-4aee-a72f-e58a5ea6fcd8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_276593b1-c176-47c2-b172-0ad63cfd7ea3" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_43180e2b-49dc-4aee-a72f-e58a5ea6fcd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_43180e2b-49dc-4aee-a72f-e58a5ea6fcd8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_43180e2b-49dc-4aee-a72f-e58a5ea6fcd8" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_43180e2b-49dc-4aee-a72f-e58a5ea6fcd8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_aab9ebed-0160-449e-8fd9-b9933600b7ef" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_43180e2b-49dc-4aee-a72f-e58a5ea6fcd8" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_aab9ebed-0160-449e-8fd9-b9933600b7ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_JrgReMember_95bc7552-2a41-49c3-b709-ab3ccc23b7e0" xlink:href="jrvr-20250331.xsd#jrvr_JrgReMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_aab9ebed-0160-449e-8fd9-b9933600b7ef" xlink:to="loc_jrvr_JrgReMember_95bc7552-2a41-49c3-b709-ab3ccc23b7e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_ccf29d4d-096a-4d10-9c57-3521d4c2a836" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_276593b1-c176-47c2-b172-0ad63cfd7ea3" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_ccf29d4d-096a-4d10-9c57-3521d4c2a836" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_ccf29d4d-096a-4d10-9c57-3521d4c2a836_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_ccf29d4d-096a-4d10-9c57-3521d4c2a836" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_ccf29d4d-096a-4d10-9c57-3521d4c2a836_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_d3253c8b-b6f4-4e51-a463-1ab5f28b7094" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_ccf29d4d-096a-4d10-9c57-3521d4c2a836" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_d3253c8b-b6f4-4e51-a463-1ab5f28b7094" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_fa132729-81de-4981-9b70-17cdd962a42f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_d3253c8b-b6f4-4e51-a463-1ab5f28b7094" xlink:to="loc_us-gaap_SubsequentEventMember_fa132729-81de-4981-9b70-17cdd962a42f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_a2abd544-9f8e-4bd5-8b49-55a57c7552bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_a2abd544-9f8e-4bd5-8b49-55a57c7552bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_26933aef-d66a-4bf5-8474-34ad5fed5845" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_26933aef-d66a-4bf5-8474-34ad5fed5845" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SellingAgreementPreCloseDividend_5ba4470d-ddd4-4a4f-960d-ea5cd6680d09" xlink:href="jrvr-20250331.xsd#jrvr_SellingAgreementPreCloseDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_jrvr_SellingAgreementPreCloseDividend_5ba4470d-ddd4-4a4f-960d-ea5cd6680d09" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment_ccf4fa7c-a2a9-4b6a-9eb7-15c09115ecd7" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment_ccf4fa7c-a2a9-4b6a-9eb7-15c09115ecd7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationAmountsOfMaterialContingentLiabilitiesRemaining_8a9ef10c-0de2-4ed1-ac5b-c2d12a922c85" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationAmountsOfMaterialContingentLiabilitiesRemaining"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationAmountsOfMaterialContingentLiabilitiesRemaining_8a9ef10c-0de2-4ed1-ac5b-c2d12a922c85" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationDownwardAdjustmentInterest_60db626d-790e-4167-aa4e-25e522056f00" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationDownwardAdjustmentInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationDownwardAdjustmentInterest_60db626d-790e-4167-aa4e-25e522056f00" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SellingAgreementPreCloseDividendForgiveness_96c83189-e756-4c2c-a237-1a96a0c5f366" xlink:href="jrvr-20250331.xsd#jrvr_SellingAgreementPreCloseDividendForgiveness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_jrvr_SellingAgreementPreCloseDividendForgiveness_96c83189-e756-4c2c-a237-1a96a0c5f366" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PaymentForSellingAgreementPreCloseDividend_b8b5c2f2-ff89-41d2-970c-c713931339ed" xlink:href="jrvr-20250331.xsd#jrvr_PaymentForSellingAgreementPreCloseDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_jrvr_PaymentForSellingAgreementPreCloseDividend_b8b5c2f2-ff89-41d2-970c-c713931339ed" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalBeforeIncomeTax_8394b748-e4ec-407b-80e9-b5330b225a2c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalBeforeIncomeTax_8394b748-e4ec-407b-80e9-b5330b225a2c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_df2ef97b-8e56-443d-80d7-e921da939a6c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_df2ef97b-8e56-443d-80d7-e921da939a6c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalNetOfTax_8751e3db-d964-4599-83bd-613a09e4b734" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalNetOfTax_8751e3db-d964-4599-83bd-613a09e4b734" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DiscontinuedOperationsTransactionCosts_9800e90f-81e6-4073-97ea-8d882f754adf" xlink:href="jrvr-20250331.xsd#jrvr_DiscontinuedOperationsTransactionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_1a3a5f65-d7cb-4224-91c5-62a1ab0b3bf3" xlink:to="loc_jrvr_DiscontinuedOperationsTransactionCosts_9800e90f-81e6-4073-97ea-8d882f754adf" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/DiscontinuedOperationsOperatingResultsofJRGReReportedinDiscontinuedOperationsDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#DiscontinuedOperationsOperatingResultsofJRGReReportedinDiscontinuedOperationsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/DiscontinuedOperationsOperatingResultsofJRGReReportedinDiscontinuedOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_067e0809-9bf2-44da-b4ca-ab38637ee720" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_222ec573-8fc6-4474-a834-c55ffbb3dfa1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_067e0809-9bf2-44da-b4ca-ab38637ee720" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_222ec573-8fc6-4474-a834-c55ffbb3dfa1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_605b8cd9-c6c8-42c6-8340-4fe891e9f243" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_222ec573-8fc6-4474-a834-c55ffbb3dfa1" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_605b8cd9-c6c8-42c6-8340-4fe891e9f243" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_605b8cd9-c6c8-42c6-8340-4fe891e9f243_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_605b8cd9-c6c8-42c6-8340-4fe891e9f243" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_605b8cd9-c6c8-42c6-8340-4fe891e9f243_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_c2ca163b-0a7d-4dbf-b365-a429574526bb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_605b8cd9-c6c8-42c6-8340-4fe891e9f243" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_c2ca163b-0a7d-4dbf-b365-a429574526bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_bb5d49cf-c47a-4bca-bf1e-ca56cd8bee39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_c2ca163b-0a7d-4dbf-b365-a429574526bb" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_bb5d49cf-c47a-4bca-bf1e-ca56cd8bee39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_567a3130-d7c0-4a6b-949c-abce8213ba11" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_222ec573-8fc6-4474-a834-c55ffbb3dfa1" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_567a3130-d7c0-4a6b-949c-abce8213ba11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_567a3130-d7c0-4a6b-949c-abce8213ba11_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_567a3130-d7c0-4a6b-949c-abce8213ba11" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_567a3130-d7c0-4a6b-949c-abce8213ba11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_a5be52d9-642f-4094-bf64-682fb4242277" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_567a3130-d7c0-4a6b-949c-abce8213ba11" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_a5be52d9-642f-4094-bf64-682fb4242277" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_JrgReMember_46df4dbc-8d67-4e97-a5e1-994821ba6008" xlink:href="jrvr-20250331.xsd#jrvr_JrgReMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_a5be52d9-642f-4094-bf64-682fb4242277" xlink:to="loc_jrvr_JrgReMember_46df4dbc-8d67-4e97-a5e1-994821ba6008" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_067e0809-9bf2-44da-b4ca-ab38637ee720" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationGrossWrittenPremiums_286d7fab-33cc-410d-8645-982eee75167e" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationGrossWrittenPremiums"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationGrossWrittenPremiums_286d7fab-33cc-410d-8645-982eee75167e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationCededPremiumsWritten_2683b1c3-1ec6-4665-bcc4-2fce240b2d61" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationCededPremiumsWritten"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationCededPremiumsWritten_2683b1c3-1ec6-4665-bcc4-2fce240b2d61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationPremiumsWrittenNet_145ab3ad-6f1d-4d58-8b97-8218746e556f" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationPremiumsWrittenNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationPremiumsWrittenNet_145ab3ad-6f1d-4d58-8b97-8218746e556f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationIncreaseDecreaseInUnearnedPremiumsNet_a7274256-184f-4c03-a4ba-947900f64b3a" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationIncreaseDecreaseInUnearnedPremiumsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationIncreaseDecreaseInUnearnedPremiumsNet_a7274256-184f-4c03-a4ba-947900f64b3a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationPremiumsEarnedNet_5fc82bec-255a-40c8-8b69-61300996300e" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationPremiumsEarnedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationPremiumsEarnedNet_5fc82bec-255a-40c8-8b69-61300996300e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationNetInvestmentIncome_ed727c24-5cb2-4efe-91d6-d868ed9fdcf8" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationNetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationNetInvestmentIncome_ed727c24-5cb2-4efe-91d6-d868ed9fdcf8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationGainLossOnInvestments_2f53ffae-fdcc-4ecb-a362-505bbbfa2059" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationGainLossOnInvestments_2f53ffae-fdcc-4ecb-a362-505bbbfa2059" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_beb2e768-35b7-4b0e-88f9-11c5ba9d2fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationRevenueAbstract_4de36b7a-a574-4a5a-aacd-eb2fb1ed2ad4" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_beb2e768-35b7-4b0e-88f9-11c5ba9d2fd1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationExpensesAbstract_84676e4f-a6a3-4fcb-8e54-ac4ceaf63d0a" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_067e0809-9bf2-44da-b4ca-ab38637ee720" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationExpensesAbstract_84676e4f-a6a3-4fcb-8e54-ac4ceaf63d0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationLossesAndLossAdjustmentExpenses_6ca45e42-3d89-47ab-9a72-e7457c12de3f" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationLossesAndLossAdjustmentExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationExpensesAbstract_84676e4f-a6a3-4fcb-8e54-ac4ceaf63d0a" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationLossesAndLossAdjustmentExpenses_6ca45e42-3d89-47ab-9a72-e7457c12de3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_c6266dca-2d6f-44e7-843c-b55036c20044" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationExpensesAbstract_84676e4f-a6a3-4fcb-8e54-ac4ceaf63d0a" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_c6266dca-2d6f-44e7-843c-b55036c20044" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense_8a5b2b45-07ea-4a49-a8b0-3e0519ac2f88" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationExpensesAbstract_84676e4f-a6a3-4fcb-8e54-ac4ceaf63d0a" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense_8a5b2b45-07ea-4a49-a8b0-3e0519ac2f88" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationTotalExpense_77d3fb23-c2b9-4396-9b54-52d79ce11045" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationTotalExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationExpensesAbstract_84676e4f-a6a3-4fcb-8e54-ac4ceaf63d0a" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationTotalExpense_77d3fb23-c2b9-4396-9b54-52d79ce11045" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_d0bae305-b462-47a1-88fc-92c5489b81cc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_067e0809-9bf2-44da-b4ca-ab38637ee720" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_d0bae305-b462-47a1-88fc-92c5489b81cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_5bd1f020-27eb-4ccc-b4eb-0ae14a95e98b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_067e0809-9bf2-44da-b4ca-ab38637ee720" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_5bd1f020-27eb-4ccc-b4eb-0ae14a95e98b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_a781792c-2559-455a-ba7b-7b581a754b44" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_067e0809-9bf2-44da-b4ca-ab38637ee720" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_a781792c-2559-455a-ba7b-7b581a754b44" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/DiscontinuedOperationsCashFlowsDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#DiscontinuedOperationsCashFlowsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/DiscontinuedOperationsCashFlowsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b9a875c3-984b-4e98-af74-f6456b347c86" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_75e641e7-3ebc-41ce-93c1-fcac9789ca9f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b9a875c3-984b-4e98-af74-f6456b347c86" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_75e641e7-3ebc-41ce-93c1-fcac9789ca9f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_d0c62603-6396-482e-909b-f5c166fc5c2e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_75e641e7-3ebc-41ce-93c1-fcac9789ca9f" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_d0c62603-6396-482e-909b-f5c166fc5c2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_d0c62603-6396-482e-909b-f5c166fc5c2e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d0c62603-6396-482e-909b-f5c166fc5c2e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_d0c62603-6396-482e-909b-f5c166fc5c2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_0750efe6-052b-46ab-96e8-b82422f3f17f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d0c62603-6396-482e-909b-f5c166fc5c2e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_0750efe6-052b-46ab-96e8-b82422f3f17f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_aaf97214-10f7-404b-a848-dfdc79df359d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_0750efe6-052b-46ab-96e8-b82422f3f17f" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_aaf97214-10f7-404b-a848-dfdc79df359d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_c1f73e31-9ba0-4f93-b7ee-cef96d1c5803" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_75e641e7-3ebc-41ce-93c1-fcac9789ca9f" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_c1f73e31-9ba0-4f93-b7ee-cef96d1c5803" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_c1f73e31-9ba0-4f93-b7ee-cef96d1c5803_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_c1f73e31-9ba0-4f93-b7ee-cef96d1c5803" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_c1f73e31-9ba0-4f93-b7ee-cef96d1c5803_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_c72b9bcd-1f47-4849-9524-a67e54633804" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_c1f73e31-9ba0-4f93-b7ee-cef96d1c5803" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_c72b9bcd-1f47-4849-9524-a67e54633804" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_JrgReMember_0dda073f-b330-4311-b5ed-f38021b96b91" xlink:href="jrvr-20250331.xsd#jrvr_JrgReMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_c72b9bcd-1f47-4849-9524-a67e54633804" xlink:to="loc_jrvr_JrgReMember_0dda073f-b330-4311-b5ed-f38021b96b91" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_2699e761-ccb2-413c-98fa-ba2789af3261" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b9a875c3-984b-4e98-af74-f6456b347c86" xlink:to="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_2699e761-ccb2-413c-98fa-ba2789af3261" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_bbb2a027-dc43-4fe1-854c-8cd5830730e7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_2699e761-ccb2-413c-98fa-ba2789af3261" xlink:to="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_bbb2a027-dc43-4fe1-854c-8cd5830730e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_0c520655-dce7-4d7f-a420-0bea4a8ee006" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_2699e761-ccb2-413c-98fa-ba2789af3261" xlink:to="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_0c520655-dce7-4d7f-a420-0bea4a8ee006" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperations_42c6fef5-610f-45d7-b87b-efb235a40498" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_2699e761-ccb2-413c-98fa-ba2789af3261" xlink:to="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperations_42c6fef5-610f-45d7-b87b-efb235a40498" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidDiscontinuedOperations_8fe64556-94e3-4d11-b9a7-4e8a5235b233" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestPaidDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_2699e761-ccb2-413c-98fa-ba2789af3261" xlink:to="loc_us-gaap_InterestPaidDiscontinuedOperations_8fe64556-94e3-4d11-b9a7-4e8a5235b233" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsScheduleofAvailableforSaleInvestmentsDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#InvestmentsScheduleofAvailableforSaleInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/InvestmentsScheduleofAvailableforSaleInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_f6ffc14e-265b-448e-a1b0-65618aedfe88" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_0a438b94-d10d-4dd2-ba73-96b4665058cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_f6ffc14e-265b-448e-a1b0-65618aedfe88" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_0a438b94-d10d-4dd2-ba73-96b4665058cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_c07ca375-a6d4-449e-a862-0991c5346614" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_0a438b94-d10d-4dd2-ba73-96b4665058cd" xlink:to="loc_us-gaap_FinancialInstrumentAxis_c07ca375-a6d4-449e-a862-0991c5346614" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c07ca375-a6d4-449e-a862-0991c5346614_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_c07ca375-a6d4-449e-a862-0991c5346614" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c07ca375-a6d4-449e-a862-0991c5346614_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_36081c31-9b57-4a6c-8235-c2d04001553c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_c07ca375-a6d4-449e-a862-0991c5346614" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_36081c31-9b57-4a6c-8235-c2d04001553c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_c367e5d0-2e40-44e0-be54-90ee7a6b88b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_36081c31-9b57-4a6c-8235-c2d04001553c" xlink:to="loc_us-gaap_DebtSecuritiesMember_c367e5d0-2e40-44e0-be54-90ee7a6b88b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_f67e115e-76f4-4e5d-8ffb-21e17e45fb4d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_c367e5d0-2e40-44e0-be54-90ee7a6b88b1" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_f67e115e-76f4-4e5d-8ffb-21e17e45fb4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_85d98661-3b74-4648-84c7-658fb14b76ea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_c367e5d0-2e40-44e0-be54-90ee7a6b88b1" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_85d98661-3b74-4648-84c7-658fb14b76ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_9a29adaf-63dc-455a-92dc-aa76976c5fc0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_c367e5d0-2e40-44e0-be54-90ee7a6b88b1" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_9a29adaf-63dc-455a-92dc-aa76976c5fc0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_3939d27a-8347-4258-8e73-263eb4b9a325" xlink:href="jrvr-20250331.xsd#jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_c367e5d0-2e40-44e0-be54-90ee7a6b88b1" xlink:to="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_3939d27a-8347-4258-8e73-263eb4b9a325" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_fa58e65e-574d-425e-a109-2a042bab0f82" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_c367e5d0-2e40-44e0-be54-90ee7a6b88b1" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_fa58e65e-574d-425e-a109-2a042bab0f82" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_e262bae9-d538-4543-bfa1-2d090ad56963" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_f6ffc14e-265b-448e-a1b0-65618aedfe88" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_e262bae9-d538-4543-bfa1-2d090ad56963" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_59288bb5-694b-441b-8a83-b1fa06ab2cee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_f6ffc14e-265b-448e-a1b0-65618aedfe88" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_59288bb5-694b-441b-8a83-b1fa06ab2cee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_873b8679-fd04-4c53-bfbd-451d4a8366f5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_f6ffc14e-265b-448e-a1b0-65618aedfe88" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_873b8679-fd04-4c53-bfbd-451d4a8366f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_c14c9b56-5937-4a8d-a25f-6f7d962f9a9b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_f6ffc14e-265b-448e-a1b0-65618aedfe88" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_c14c9b56-5937-4a8d-a25f-6f7d962f9a9b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsScheduleofGrossUnrealizedLossesandFairValueDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#InvestmentsScheduleofGrossUnrealizedLossesandFairValueDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/InvestmentsScheduleofGrossUnrealizedLossesandFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_34946c24-9074-41c4-8009-efc79896fe22" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_34946c24-9074-41c4-8009-efc79896fe22" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_d7ab1b83-9569-47b7-8b1b-728fbd4e59a9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_34946c24-9074-41c4-8009-efc79896fe22" xlink:to="loc_us-gaap_FinancialInstrumentAxis_d7ab1b83-9569-47b7-8b1b-728fbd4e59a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d7ab1b83-9569-47b7-8b1b-728fbd4e59a9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_d7ab1b83-9569-47b7-8b1b-728fbd4e59a9" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d7ab1b83-9569-47b7-8b1b-728fbd4e59a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4c89c66d-e258-406d-8126-55a54424ef18" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_d7ab1b83-9569-47b7-8b1b-728fbd4e59a9" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4c89c66d-e258-406d-8126-55a54424ef18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_d0bb9200-5e39-4c37-873d-fcf31d850f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4c89c66d-e258-406d-8126-55a54424ef18" xlink:to="loc_us-gaap_DebtSecuritiesMember_d0bb9200-5e39-4c37-873d-fcf31d850f1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_52ac2c0c-dfa6-4881-9b98-c0261489423b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_d0bb9200-5e39-4c37-873d-fcf31d850f1a" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_52ac2c0c-dfa6-4881-9b98-c0261489423b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_0f92ac71-fd0e-40a8-a29b-35e8db461255" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_d0bb9200-5e39-4c37-873d-fcf31d850f1a" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_0f92ac71-fd0e-40a8-a29b-35e8db461255" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_3b540029-afb0-4510-937b-40acf9198070" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_d0bb9200-5e39-4c37-873d-fcf31d850f1a" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_3b540029-afb0-4510-937b-40acf9198070" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_c9202c5d-981d-47c6-b4ff-a393292c3007" xlink:href="jrvr-20250331.xsd#jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_d0bb9200-5e39-4c37-873d-fcf31d850f1a" xlink:to="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_c9202c5d-981d-47c6-b4ff-a393292c3007" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_526c686c-fd81-41df-944c-f8e8cdf01f08" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_d0bb9200-5e39-4c37-873d-fcf31d850f1a" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_526c686c-fd81-41df-944c-f8e8cdf01f08" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_ce0ca03c-0902-4300-9b7a-f9e515fb55c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_ce0ca03c-0902-4300-9b7a-f9e515fb55c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_0110c993-4118-42dc-952a-71f30690b1e2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_0110c993-4118-42dc-952a-71f30690b1e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_6a69b342-5271-4a36-be97-eea777558b30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_6a69b342-5271-4a36-be97-eea777558b30" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_72a069c5-cb04-4fca-b726-2e4a12861548" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_72a069c5-cb04-4fca-b726-2e4a12861548" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_dc2f54c2-8f64-4b2f-8e03-f19c33e6bbf5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_dc2f54c2-8f64-4b2f-8e03-f19c33e6bbf5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_b0512327-2cf0-44b2-a5c3-a6cbf2c0b0b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_10118d93-f0c1-47c1-bfc8-5a02fb3ddd4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_b0512327-2cf0-44b2-a5c3-a6cbf2c0b0b9" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#InvestmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/InvestmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_cb830c00-026a-4ecd-9c6a-37070b3109dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfGainLossOnInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_cb830c00-026a-4ecd-9c6a-37070b3109dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_998e2d08-264e-41d2-9e06-4b058bd96e1f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_cb830c00-026a-4ecd-9c6a-37070b3109dc" xlink:to="loc_us-gaap_FinancialInstrumentAxis_998e2d08-264e-41d2-9e06-4b058bd96e1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_998e2d08-264e-41d2-9e06-4b058bd96e1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_998e2d08-264e-41d2-9e06-4b058bd96e1f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_998e2d08-264e-41d2-9e06-4b058bd96e1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_05c358cb-54c3-4d3f-8e14-2c2d95f4c275" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_998e2d08-264e-41d2-9e06-4b058bd96e1f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_05c358cb-54c3-4d3f-8e14-2c2d95f4c275" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_49e95c21-a465-4443-af2e-cc8b5c601025" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_05c358cb-54c3-4d3f-8e14-2c2d95f4c275" xlink:to="loc_us-gaap_DebtSecuritiesMember_49e95c21-a465-4443-af2e-cc8b5c601025" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingStandardPoorsAxis_90f62b0b-b18e-4edf-8edd-caf6ad6572c6" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CreditRatingStandardPoorsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_cb830c00-026a-4ecd-9c6a-37070b3109dc" xlink:to="loc_srt_CreditRatingStandardPoorsAxis_90f62b0b-b18e-4edf-8edd-caf6ad6572c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ExternalCreditRatingStandardPoorsMember_90f62b0b-b18e-4edf-8edd-caf6ad6572c6_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ExternalCreditRatingStandardPoorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CreditRatingStandardPoorsAxis_90f62b0b-b18e-4edf-8edd-caf6ad6572c6" xlink:to="loc_srt_ExternalCreditRatingStandardPoorsMember_90f62b0b-b18e-4edf-8edd-caf6ad6572c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ExternalCreditRatingStandardPoorsMember_5ebbfc59-eab5-4eab-b652-235a99a5b4f0" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ExternalCreditRatingStandardPoorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CreditRatingStandardPoorsAxis_90f62b0b-b18e-4edf-8edd-caf6ad6572c6" xlink:to="loc_srt_ExternalCreditRatingStandardPoorsMember_5ebbfc59-eab5-4eab-b652-235a99a5b4f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_StandardPoorsBBBorBetterRatingMember_303397ac-4531-4bd5-a6a6-7b211c433091" xlink:href="jrvr-20250331.xsd#jrvr_StandardPoorsBBBorBetterRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ExternalCreditRatingStandardPoorsMember_5ebbfc59-eab5-4eab-b652-235a99a5b4f0" xlink:to="loc_jrvr_StandardPoorsBBBorBetterRatingMember_303397ac-4531-4bd5-a6a6-7b211c433091" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_70d9c7af-4d69-493b-a19f-4c2dcdea8855" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_70d9c7af-4d69-493b-a19f-4c2dcdea8855" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_17463cc4-7388-4f90-8d4f-fcb11f47accf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_17463cc4-7388-4f90-8d4f-fcb11f47accf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_ff3d2534-a1c9-4ae8-a292-93109fe2af4b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_ff3d2534-a1c9-4ae8-a292-93109fe2af4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PercentageOfAvailableForSaleDebtSecurities_7889a2ec-73c7-4168-b14f-3ccc3ae22c71" xlink:href="jrvr-20250331.xsd#jrvr_PercentageOfAvailableForSaleDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_jrvr_PercentageOfAvailableForSaleDebtSecurities_7889a2ec-73c7-4168-b14f-3ccc3ae22c71" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_182d0a9e-56a6-4c18-a2ae-71a53a4ea0a9" xlink:href="jrvr-20250331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_182d0a9e-56a6-4c18-a2ae-71a53a4ea0a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance_ec77bb83-047b-4b93-b6bd-68e4efdbfd23" xlink:href="jrvr-20250331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance_ec77bb83-047b-4b93-b6bd-68e4efdbfd23" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_74f458ea-fc70-474b-820a-a7c608ee9c88" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_74f458ea-fc70-474b-820a-a7c608ee9c88" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_BankLoanParticipationsNetGainLoss_37850f6b-dfaa-413c-85dd-2868bb62c253" xlink:href="jrvr-20250331.xsd#jrvr_BankLoanParticipationsNetGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_jrvr_BankLoanParticipationsNetGainLoss_37850f6b-dfaa-413c-85dd-2868bb62c253" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_BankLoanParticipationsRealizedAndUnrealizedLossesCreditRelatedImpairments_4b2d464a-1110-4ca7-b5a1-f1cb7fe5faa8" xlink:href="jrvr-20250331.xsd#jrvr_BankLoanParticipationsRealizedAndUnrealizedLossesCreditRelatedImpairments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_7bd7627e-3a30-42bd-8942-2b4693892f14" xlink:to="loc_jrvr_BankLoanParticipationsRealizedAndUnrealizedLossesCreditRelatedImpairments_4b2d464a-1110-4ca7-b5a1-f1cb7fe5faa8" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsScheduleofPrivateDebtandEquityDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#InvestmentsScheduleofPrivateDebtandEquityDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/InvestmentsScheduleofPrivateDebtandEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_5b563841-4da9-4446-a370-fdff3b06c5ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_5b563841-4da9-4446-a370-fdff3b06c5ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_db339a33-43c4-41dd-ba0f-57e58ee64617" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_5b563841-4da9-4446-a370-fdff3b06c5ec" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_db339a33-43c4-41dd-ba0f-57e58ee64617" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_db339a33-43c4-41dd-ba0f-57e58ee64617_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_db339a33-43c4-41dd-ba0f-57e58ee64617" xlink:to="loc_us-gaap_SegmentDomain_db339a33-43c4-41dd-ba0f-57e58ee64617_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_f771e460-e960-4caa-9bed-adbb3cb001df" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_db339a33-43c4-41dd-ba0f-57e58ee64617" xlink:to="loc_us-gaap_SegmentDomain_f771e460-e960-4caa-9bed-adbb3cb001df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_3d3eaf0f-16dd-4b7c-9dc2-e9baef719146" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_f771e460-e960-4caa-9bed-adbb3cb001df" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_3d3eaf0f-16dd-4b7c-9dc2-e9baef719146" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_a25106b9-b880-4d55-a07b-9b8ecaa20a18" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_f771e460-e960-4caa-9bed-adbb3cb001df" xlink:to="loc_us-gaap_CorporateAndOtherMember_a25106b9-b880-4d55-a07b-9b8ecaa20a18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_a7e11092-228f-4bf2-a03c-c0b68ac3b605" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_5b563841-4da9-4446-a370-fdff3b06c5ec" xlink:to="loc_us-gaap_InvestmentTypeAxis_a7e11092-228f-4bf2-a03c-c0b68ac3b605" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_a7e11092-228f-4bf2-a03c-c0b68ac3b605_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_a7e11092-228f-4bf2-a03c-c0b68ac3b605" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_a7e11092-228f-4bf2-a03c-c0b68ac3b605_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_405be512-429a-489f-86c9-18e9ac8dcafa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_a7e11092-228f-4bf2-a03c-c0b68ac3b605" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_405be512-429a-489f-86c9-18e9ac8dcafa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RenewableEnergyLlcsMember_b754ddf6-5bb7-417f-a665-52cdef0e079c" xlink:href="jrvr-20250331.xsd#jrvr_RenewableEnergyLlcsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_405be512-429a-489f-86c9-18e9ac8dcafa" xlink:to="loc_jrvr_RenewableEnergyLlcsMember_b754ddf6-5bb7-417f-a665-52cdef0e079c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RenewableEnergyBridgeFinancingNotesMember_f7ac3dca-5086-4045-99c6-9e9c3713493d" xlink:href="jrvr-20250331.xsd#jrvr_RenewableEnergyBridgeFinancingNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_405be512-429a-489f-86c9-18e9ac8dcafa" xlink:to="loc_jrvr_RenewableEnergyBridgeFinancingNotesMember_f7ac3dca-5086-4045-99c6-9e9c3713493d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_2a0b0eb5-3304-4d45-af7b-835d533c4b05" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_405be512-429a-489f-86c9-18e9ac8dcafa" xlink:to="loc_srt_PartnershipInterestMember_2a0b0eb5-3304-4d45-af7b-835d533c4b05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PrivateDebtMember_cd9c8b9e-e2d6-44c2-9f44-715886a09fdf" xlink:href="jrvr-20250331.xsd#jrvr_PrivateDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_405be512-429a-489f-86c9-18e9ac8dcafa" xlink:to="loc_jrvr_PrivateDebtMember_cd9c8b9e-e2d6-44c2-9f44-715886a09fdf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PrivateSpecialityCreditMember_39c3c936-5659-4c52-a499-93ec53db9e03" xlink:href="jrvr-20250331.xsd#jrvr_PrivateSpecialityCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_PrivateDebtMember_cd9c8b9e-e2d6-44c2-9f44-715886a09fdf" xlink:to="loc_jrvr_PrivateSpecialityCreditMember_39c3c936-5659-4c52-a499-93ec53db9e03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_0bf3ea63-df9e-4f96-a904-90a7ea6263d0" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_5b563841-4da9-4446-a370-fdff3b06c5ec" xlink:to="loc_srt_RangeAxis_0bf3ea63-df9e-4f96-a904-90a7ea6263d0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0bf3ea63-df9e-4f96-a904-90a7ea6263d0_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_0bf3ea63-df9e-4f96-a904-90a7ea6263d0" xlink:to="loc_srt_RangeMember_0bf3ea63-df9e-4f96-a904-90a7ea6263d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0d781bc8-cf53-40ee-9b3d-ceb23629191f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_0bf3ea63-df9e-4f96-a904-90a7ea6263d0" xlink:to="loc_srt_RangeMember_0d781bc8-cf53-40ee-9b3d-ceb23629191f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_ebaed22e-7de7-4a38-a210-e05f333108fb" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_0d781bc8-cf53-40ee-9b3d-ceb23629191f" xlink:to="loc_srt_MinimumMember_ebaed22e-7de7-4a38-a210-e05f333108fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_53f144fc-01f8-4215-9bd6-9c203af0b852" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_0d781bc8-cf53-40ee-9b3d-ceb23629191f" xlink:to="loc_srt_MaximumMember_53f144fc-01f8-4215-9bd6-9c203af0b852" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_cce0f6c4-df04-4a80-9f3e-2ebaa17dbc83" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_5b563841-4da9-4446-a370-fdff3b06c5ec" xlink:to="loc_us-gaap_FinancialInstrumentAxis_cce0f6c4-df04-4a80-9f3e-2ebaa17dbc83" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_cce0f6c4-df04-4a80-9f3e-2ebaa17dbc83_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_cce0f6c4-df04-4a80-9f3e-2ebaa17dbc83" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_cce0f6c4-df04-4a80-9f3e-2ebaa17dbc83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_bfc83371-9dd5-4be0-8819-531d9bca851b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_cce0f6c4-df04-4a80-9f3e-2ebaa17dbc83" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_bfc83371-9dd5-4be0-8819-531d9bca851b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_InvestmentInLlcMember_3a718225-2d04-4a55-b3f4-f699e7bd3f46" xlink:href="jrvr-20250331.xsd#jrvr_InvestmentInLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_bfc83371-9dd5-4be0-8819-531d9bca851b" xlink:to="loc_jrvr_InvestmentInLlcMember_3a718225-2d04-4a55-b3f4-f699e7bd3f46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableOneMember_c7e4c6b5-fa3c-4cca-9a55-ce18c9f8c958" xlink:href="jrvr-20250331.xsd#jrvr_NotesReceivableOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_bfc83371-9dd5-4be0-8819-531d9bca851b" xlink:to="loc_jrvr_NotesReceivableOneMember_c7e4c6b5-fa3c-4cca-9a55-ce18c9f8c958" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableTwoMember_29676b4e-5d8a-4127-b030-e4217ec18d40" xlink:href="jrvr-20250331.xsd#jrvr_NotesReceivableTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_bfc83371-9dd5-4be0-8819-531d9bca851b" xlink:to="loc_jrvr_NotesReceivableTwoMember_29676b4e-5d8a-4127-b030-e4217ec18d40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableThreeMember_d54c3c25-0306-4ba9-9048-c8c5bb11fdb1" xlink:href="jrvr-20250331.xsd#jrvr_NotesReceivableThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_bfc83371-9dd5-4be0-8819-531d9bca851b" xlink:to="loc_jrvr_NotesReceivableThreeMember_d54c3c25-0306-4ba9-9048-c8c5bb11fdb1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableFourMember_91ac8ecb-cae9-4279-be46-9be850162844" xlink:href="jrvr-20250331.xsd#jrvr_NotesReceivableFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_bfc83371-9dd5-4be0-8819-531d9bca851b" xlink:to="loc_jrvr_NotesReceivableFourMember_91ac8ecb-cae9-4279-be46-9be850162844" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_30ca945c-0874-4db0-9795-39b110404449" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_5b563841-4da9-4446-a370-fdff3b06c5ec" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_30ca945c-0874-4db0-9795-39b110404449" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_30ca945c-0874-4db0-9795-39b110404449_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_30ca945c-0874-4db0-9795-39b110404449" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_30ca945c-0874-4db0-9795-39b110404449_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_c9465d7e-3d02-4a58-a82b-dc1d585f220b" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_30ca945c-0874-4db0-9795-39b110404449" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_c9465d7e-3d02-4a58-a82b-dc1d585f220b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_VariousLLCsMember_553e9411-b515-445c-b57c-46411fdb64cb" xlink:href="jrvr-20250331.xsd#jrvr_VariousLLCsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_c9465d7e-3d02-4a58-a82b-dc1d585f220b" xlink:to="loc_jrvr_VariousLLCsMember_553e9411-b515-445c-b57c-46411fdb64cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInvestments_0e04210c-897d-41de-bb4f-ae7d8d241c71" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_OtherInvestments_0e04210c-897d-41de-bb4f-ae7d8d241c71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_46311cce-d10e-469f-9d73-843cc8b61e48" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_46311cce-d10e-469f-9d73-843cc8b61e48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeNet_c352d351-dd82-4a06-97ba-207a10a77fa3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIncomeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_InvestmentIncomeNet_c352d351-dd82-4a06-97ba-207a10a77fa3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_a7b21867-04f5-451a-84db-ebf47a09630c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_a7b21867-04f5-451a-84db-ebf47a09630c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentDividendsOrDistributions_72c6355d-c996-483c-9ec0-14d9db3e0e9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityMethodInvestmentDividendsOrDistributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_EquityMethodInvestmentDividendsOrDistributions_72c6355d-c996-483c-9ec0-14d9db3e0e9e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfNotesIssued_e0809f3d-c789-4026-8881-bfd4b9ec37b9" xlink:href="jrvr-20250331.xsd#jrvr_NumberOfNotesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_jrvr_NumberOfNotesIssued_e0809f3d-c789-4026-8881-bfd4b9ec37b9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRate_877984a7-2ea3-4540-907d-afc32dd79950" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_InvestmentInterestRate_877984a7-2ea3-4540-907d-afc32dd79950" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments_ecd673d8-260f-4ee6-bcd5-4cd3cf3e6240" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments_ecd673d8-260f-4ee6-bcd5-4cd3cf3e6240" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommitmentToInvestmentInLimitedPartnership_e734df3e-7e52-476c-acb1-fb6b3c1ae3f4" xlink:href="jrvr-20250331.xsd#jrvr_CommitmentToInvestmentInLimitedPartnership"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_jrvr_CommitmentToInvestmentInLimitedPartnership_e734df3e-7e52-476c-acb1-fb6b3c1ae3f4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommitmentToInvestmentInNotes_25b297ec-5400-49a8-bf11-ff1e2e6aea1b" xlink:href="jrvr-20250331.xsd#jrvr_CommitmentToInvestmentInNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_0f0cf0c1-9db0-48c3-8652-64428086d887" xlink:to="loc_jrvr_CommitmentToInvestmentInNotes_25b297ec-5400-49a8-bf11-ff1e2e6aea1b" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/GoodwillandIntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#GoodwillandIntangibleAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/GoodwillandIntangibleAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_ce615cc5-ff9a-48a5-9651-6c8f22e41d2b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_3c349c5b-d698-4540-a89e-0fda3737bbd5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_ce615cc5-ff9a-48a5-9651-6c8f22e41d2b" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_3c349c5b-d698-4540-a89e-0fda3737bbd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_ad83a6e6-53dc-4df4-9ba7-bcc99d3ffc30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_3c349c5b-d698-4540-a89e-0fda3737bbd5" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_ad83a6e6-53dc-4df4-9ba7-bcc99d3ffc30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_ad83a6e6-53dc-4df4-9ba7-bcc99d3ffc30_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_ad83a6e6-53dc-4df4-9ba7-bcc99d3ffc30" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_ad83a6e6-53dc-4df4-9ba7-bcc99d3ffc30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3d02bfb3-7b3c-404b-937f-d252df23daee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_ad83a6e6-53dc-4df4-9ba7-bcc99d3ffc30" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3d02bfb3-7b3c-404b-937f-d252df23daee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_JamesRiverGroupIncMember_f5925b0d-29dd-4ba4-a7e7-1dc3289722a2" xlink:href="jrvr-20250331.xsd#jrvr_JamesRiverGroupIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3d02bfb3-7b3c-404b-937f-d252df23daee" xlink:to="loc_jrvr_JamesRiverGroupIncMember_f5925b0d-29dd-4ba4-a7e7-1dc3289722a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_912dfe29-cf93-4ee2-a10d-be1c8703d066" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_ce615cc5-ff9a-48a5-9651-6c8f22e41d2b" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_912dfe29-cf93-4ee2-a10d-be1c8703d066" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_fa7e7194-8b25-48fe-8177-cf0ba3d17903" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_ce615cc5-ff9a-48a5-9651-6c8f22e41d2b" xlink:to="loc_us-gaap_Goodwill_fa7e7194-8b25-48fe-8177-cf0ba3d17903" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/GoodwillandIntangibleAssetsScheduleofGoodwillandIntangibleAssetsDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#GoodwillandIntangibleAssetsScheduleofGoodwillandIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/GoodwillandIntangibleAssetsScheduleofGoodwillandIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AcquiredIntangibleAssetsLineItems_3b20f27f-25f1-4d45-aa44-2fe42c51299a" xlink:href="jrvr-20250331.xsd#jrvr_AcquiredIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_ffb99f43-d283-427b-895b-6bb10cb049a3" xlink:href="jrvr-20250331.xsd#jrvr_ScheduleOfAcquiredIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_3b20f27f-25f1-4d45-aa44-2fe42c51299a" xlink:to="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_ffb99f43-d283-427b-895b-6bb10cb049a3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_d30fd217-16f6-4513-9de1-9ba7ad3641d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_ffb99f43-d283-427b-895b-6bb10cb049a3" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_d30fd217-16f6-4513-9de1-9ba7ad3641d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_d30fd217-16f6-4513-9de1-9ba7ad3641d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_d30fd217-16f6-4513-9de1-9ba7ad3641d4" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_d30fd217-16f6-4513-9de1-9ba7ad3641d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_f4234fa5-af0d-4fc9-a96c-3d22a030451c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_d30fd217-16f6-4513-9de1-9ba7ad3641d4" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_f4234fa5-af0d-4fc9-a96c-3d22a030451c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksMember_186332aa-4430-40c8-b40b-65d9ba5c45cb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TrademarksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_f4234fa5-af0d-4fc9-a96c-3d22a030451c" xlink:to="loc_us-gaap_TrademarksMember_186332aa-4430-40c8-b40b-65d9ba5c45cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicensingAgreementsMember_f4e3bc04-6e71-4662-9d8d-df44e3808671" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LicensingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_f4234fa5-af0d-4fc9-a96c-3d22a030451c" xlink:to="loc_us-gaap_LicensingAgreementsMember_f4e3bc04-6e71-4662-9d8d-df44e3808671" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_62228fb7-639c-4c25-bf41-d5911ee3ab62" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_ffb99f43-d283-427b-895b-6bb10cb049a3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_62228fb7-639c-4c25-bf41-d5911ee3ab62" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_62228fb7-639c-4c25-bf41-d5911ee3ab62_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_62228fb7-639c-4c25-bf41-d5911ee3ab62" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_62228fb7-639c-4c25-bf41-d5911ee3ab62_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1d25cbfb-8649-4efd-aae3-a1fdcf4df972" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_62228fb7-639c-4c25-bf41-d5911ee3ab62" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1d25cbfb-8649-4efd-aae3-a1fdcf4df972" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_BrokerRelationshipsMember_cdb40325-d2d0-4a74-ac71-d3204db103a3" xlink:href="jrvr-20250331.xsd#jrvr_BrokerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1d25cbfb-8649-4efd-aae3-a1fdcf4df972" xlink:to="loc_jrvr_BrokerRelationshipsMember_cdb40325-d2d0-4a74-ac71-d3204db103a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_c11de7b1-f9e2-4b48-8c64-e29eef371150" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_3b20f27f-25f1-4d45-aa44-2fe42c51299a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_c11de7b1-f9e2-4b48-8c64-e29eef371150" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_f127e87f-8ff2-4384-b8b5-8c9bddbb3c99" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_3b20f27f-25f1-4d45-aa44-2fe42c51299a" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_f127e87f-8ff2-4384-b8b5-8c9bddbb3c99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_565f45e2-7c06-43ce-b02f-afc6e69c8f73" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_3b20f27f-25f1-4d45-aa44-2fe42c51299a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_565f45e2-7c06-43ce-b02f-afc6e69c8f73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_c61639e0-16c8-4d42-978e-4897c92d1f08" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_565f45e2-7c06-43ce-b02f-afc6e69c8f73" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_c61639e0-16c8-4d42-978e-4897c92d1f08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_56ebb09b-d5e6-4cf2-80f6-df4476e92839" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_565f45e2-7c06-43ce-b02f-afc6e69c8f73" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_56ebb09b-d5e6-4cf2-80f6-df4476e92839" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_3eb62dee-79ac-4327-b4c6-c67f4028f415" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_3b20f27f-25f1-4d45-aa44-2fe42c51299a" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_3eb62dee-79ac-4327-b4c6-c67f4028f415" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#ReserveforLossesandLossAdjustmentExpensesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:href="jrvr-20250331.xsd#jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_522ca454-7ff2-4c07-b143-6f239b6c90b4" xlink:href="jrvr-20250331.xsd#jrvr_ReserveForLossesAndLossAdjustmentExpensesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_522ca454-7ff2-4c07-b143-6f239b6c90b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_d425a453-e9e4-40ff-a3af-d3294e22d953" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_522ca454-7ff2-4c07-b143-6f239b6c90b4" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_d425a453-e9e4-40ff-a3af-d3294e22d953" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_d425a453-e9e4-40ff-a3af-d3294e22d953_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_d425a453-e9e4-40ff-a3af-d3294e22d953" xlink:to="loc_us-gaap_SegmentDomain_d425a453-e9e4-40ff-a3af-d3294e22d953_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_c8050a40-809e-44e0-83bd-3e5e2f847aae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_d425a453-e9e4-40ff-a3af-d3294e22d953" xlink:to="loc_us-gaap_SegmentDomain_c8050a40-809e-44e0-83bd-3e5e2f847aae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_9f284f5f-7b9b-472c-bbff-8431abd5c0cd" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c8050a40-809e-44e0-83bd-3e5e2f847aae" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_9f284f5f-7b9b-472c-bbff-8431abd5c0cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SpecialtyAdmittedInsuranceMember_1dc84c85-940f-4031-9a62-9a229579be5e" xlink:href="jrvr-20250331.xsd#jrvr_SpecialtyAdmittedInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c8050a40-809e-44e0-83bd-3e5e2f847aae" xlink:to="loc_jrvr_SpecialtyAdmittedInsuranceMember_1dc84c85-940f-4031-9a62-9a229579be5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_c32918af-f9c0-40f8-bc8e-3f52a19bcf7e" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_522ca454-7ff2-4c07-b143-6f239b6c90b4" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_c32918af-f9c0-40f8-bc8e-3f52a19bcf7e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_c32918af-f9c0-40f8-bc8e-3f52a19bcf7e_default" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_c32918af-f9c0-40f8-bc8e-3f52a19bcf7e" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_c32918af-f9c0-40f8-bc8e-3f52a19bcf7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_f2e2497d-4b06-4429-bda4-63b6ee5ed8f4" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_c32918af-f9c0-40f8-bc8e-3f52a19bcf7e" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_f2e2497d-4b06-4429-bda4-63b6ee5ed8f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LossPortfolioTransferMember_db3ae954-ae95-46f9-a495-d6c3b15fee32" xlink:href="jrvr-20250331.xsd#jrvr_LossPortfolioTransferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_f2e2497d-4b06-4429-bda4-63b6ee5ed8f4" xlink:to="loc_jrvr_LossPortfolioTransferMember_db3ae954-ae95-46f9-a495-d6c3b15fee32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ESADCAgreementMember_6c708032-7ee0-451a-9461-4ed5eb57db6c" xlink:href="jrvr-20250331.xsd#jrvr_ESADCAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_f2e2497d-4b06-4429-bda4-63b6ee5ed8f4" xlink:to="loc_jrvr_ESADCAgreementMember_6c708032-7ee0-451a-9461-4ed5eb57db6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ESTopUpADCMember_9c215428-5804-4061-a9e4-e66c3306cf58" xlink:href="jrvr-20250331.xsd#jrvr_ESTopUpADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_f2e2497d-4b06-4429-bda4-63b6ee5ed8f4" xlink:to="loc_jrvr_ESTopUpADCMember_9c215428-5804-4061-a9e4-e66c3306cf58" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_8f83a6c7-18f5-4b7b-8894-34a3f2f007bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_522ca454-7ff2-4c07-b143-6f239b6c90b4" xlink:to="loc_us-gaap_SubsegmentsAxis_8f83a6c7-18f5-4b7b-8894-34a3f2f007bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_8f83a6c7-18f5-4b7b-8894-34a3f2f007bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_8f83a6c7-18f5-4b7b-8894-34a3f2f007bc" xlink:to="loc_us-gaap_SubsegmentsDomain_8f83a6c7-18f5-4b7b-8894-34a3f2f007bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_057b28cc-179f-495a-aa6c-52d7f2a9a22d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_8f83a6c7-18f5-4b7b-8894-34a3f2f007bc" xlink:to="loc_us-gaap_SubsegmentsDomain_057b28cc-179f-495a-aa6c-52d7f2a9a22d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoBusinessMember_cd077900-0648-4d68-84a0-c12ca1bbca7c" xlink:href="jrvr-20250331.xsd#jrvr_CommercialAutoBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_057b28cc-179f-495a-aa6c-52d7f2a9a22d" xlink:to="loc_jrvr_CommercialAutoBusinessMember_cd077900-0648-4d68-84a0-c12ca1bbca7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1e16737b-a194-4dfe-9ac3-5568ac02bb97" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_522ca454-7ff2-4c07-b143-6f239b6c90b4" xlink:to="loc_dei_LegalEntityAxis_1e16737b-a194-4dfe-9ac3-5568ac02bb97" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1e16737b-a194-4dfe-9ac3-5568ac02bb97_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1e16737b-a194-4dfe-9ac3-5568ac02bb97" xlink:to="loc_dei_EntityDomain_1e16737b-a194-4dfe-9ac3-5568ac02bb97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_af0911ee-3727-466a-b2f8-88ee8ba16ef4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1e16737b-a194-4dfe-9ac3-5568ac02bb97" xlink:to="loc_dei_EntityDomain_af0911ee-3727-466a-b2f8-88ee8ba16ef4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_StateNationalMember_bd0ba0d6-1f07-4c0f-9ccf-6cfb9cc6b681" xlink:href="jrvr-20250331.xsd#jrvr_StateNationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_af0911ee-3727-466a-b2f8-88ee8ba16ef4" xlink:to="loc_jrvr_StateNationalMember_bd0ba0d6-1f07-4c0f-9ccf-6cfb9cc6b681" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_8bfe88e5-c31d-461c-850c-6ecd37649000" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_8bfe88e5-c31d-461c-850c-6ecd37649000" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_38f9eaab-7280-459b-a9a0-1bb7a253c135" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_38f9eaab-7280-459b-a9a0-1bb7a253c135" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CumulativeAmountsCededUnderLossPortfolioTransfer_3acdd371-a60c-4b8f-8c03-eb015dd09853" xlink:href="jrvr-20250331.xsd#jrvr_CumulativeAmountsCededUnderLossPortfolioTransfer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_jrvr_CumulativeAmountsCededUnderLossPortfolioTransfer_3acdd371-a60c-4b8f-8c03-eb015dd09853" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage_680eaed4-64ba-4e6a-9e9f-cfb6e2772a57" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage_680eaed4-64ba-4e6a-9e9f-cfb6e2772a57" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsureExcessAmount_06ebcc38-75a6-4406-9093-3c72a1bf9915" xlink:href="jrvr-20250331.xsd#jrvr_ReinsureExcessAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_jrvr_ReinsureExcessAmount_06ebcc38-75a6-4406-9093-3c72a1bf9915" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceAggregateCoverageLimit_ddef7a42-fd94-48f6-bedd-9766debe2d59" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceAggregateCoverageLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_jrvr_ReinsuranceAggregateCoverageLimit_ddef7a42-fd94-48f6-bedd-9766debe2d59" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForReinsurance_1db31a04-15c5-483e-a473-28be9e9ec404" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsForReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_us-gaap_PaymentsForReinsurance_1db31a04-15c5-483e-a473-28be9e9ec404" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceAggregateCoverageLimitAmountRemaining_b285be87-4d41-4a5d-80f8-c506b6ecdbaa" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceAggregateCoverageLimitAmountRemaining"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_jrvr_ReinsuranceAggregateCoverageLimitAmountRemaining_b285be87-4d41-4a5d-80f8-c506b6ecdbaa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_ca5294b3-d45f-4391-9669-b3fb21fb2f39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_c9ff61b4-4c11-4be7-b79a-9d0a3e4a8f70" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_ca5294b3-d45f-4391-9669-b3fb21fb2f39" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesReserveforLossesandLossAdjustmentExpensesNetofReinsuranceDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#ReserveforLossesandLossAdjustmentExpensesReserveforLossesandLossAdjustmentExpensesNetofReinsuranceDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesReserveforLossesandLossAdjustmentExpensesNetofReinsuranceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_d5b1ebe8-fc12-4b2f-a3af-f3172b638b2e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_36cf77bb-d1af-46e2-bffe-20c058e87fa8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_d5b1ebe8-fc12-4b2f-a3af-f3172b638b2e" xlink:to="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_36cf77bb-d1af-46e2-bffe-20c058e87fa8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_2a01f8ec-7619-4a2a-b10d-38e9787048c6" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_36cf77bb-d1af-46e2-bffe-20c058e87fa8" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_2a01f8ec-7619-4a2a-b10d-38e9787048c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_2a01f8ec-7619-4a2a-b10d-38e9787048c6_default" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_2a01f8ec-7619-4a2a-b10d-38e9787048c6" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_2a01f8ec-7619-4a2a-b10d-38e9787048c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_ec9ed814-4892-4b22-8353-d2bd350a3a33" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_2a01f8ec-7619-4a2a-b10d-38e9787048c6" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_ec9ed814-4892-4b22-8353-d2bd350a3a33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoLPTAndESADCMember_e182f96c-76b5-41e8-9cb3-375d7dc1a726" xlink:href="jrvr-20250331.xsd#jrvr_CommercialAutoLPTAndESADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_ec9ed814-4892-4b22-8353-d2bd350a3a33" xlink:to="loc_jrvr_CommercialAutoLPTAndESADCMember_e182f96c-76b5-41e8-9cb3-375d7dc1a726" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_2e450a61-3320-43d5-94b2-dd22a6923ed7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_36cf77bb-d1af-46e2-bffe-20c058e87fa8" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_2e450a61-3320-43d5-94b2-dd22a6923ed7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_2e450a61-3320-43d5-94b2-dd22a6923ed7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2e450a61-3320-43d5-94b2-dd22a6923ed7" xlink:to="loc_us-gaap_SegmentDomain_2e450a61-3320-43d5-94b2-dd22a6923ed7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_cfdc8111-3b74-40f4-90ab-a0b9591cbb80" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2e450a61-3320-43d5-94b2-dd22a6923ed7" xlink:to="loc_us-gaap_SegmentDomain_cfdc8111-3b74-40f4-90ab-a0b9591cbb80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_a378e2ed-55f8-45f4-b520-da404794ce31" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cfdc8111-3b74-40f4-90ab-a0b9591cbb80" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_a378e2ed-55f8-45f4-b520-da404794ce31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_d5b1ebe8-fc12-4b2f-a3af-f3172b638b2e" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_729aa44e-87cf-4f35-afff-3d365e6a425e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_729aa44e-87cf-4f35-afff-3d365e6a425e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_9cbb70a5-205a-472d-b79a-6f3c0b6fb74b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_9cbb70a5-205a-472d-b79a-6f3c0b6fb74b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_cc11b1b9-487e-4353-b5d4-c97df4c22a61" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_9cbb70a5-205a-472d-b79a-6f3c0b6fb74b" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_cc11b1b9-487e-4353-b5d4-c97df4c22a61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_aec79a19-4fe5-4b41-84a2-feaf0ef925a1" xlink:href="jrvr-20250331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_9cbb70a5-205a-472d-b79a-6f3c0b6fb74b" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_aec79a19-4fe5-4b41-84a2-feaf0ef925a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_0b64f86a-7fb4-4a83-9f6d-c549e1284a8f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_9cbb70a5-205a-472d-b79a-6f3c0b6fb74b" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_0b64f86a-7fb4-4a83-9f6d-c549e1284a8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_36552ae4-8e86-494d-8ab7-a1b760c6c47e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_9cbb70a5-205a-472d-b79a-6f3c0b6fb74b" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_36552ae4-8e86-494d-8ab7-a1b760c6c47e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_33bf7583-8e0e-4b30-a8bb-e5c2308a2bac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_33bf7583-8e0e-4b30-a8bb-e5c2308a2bac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1_46fa66be-f99b-4479-ac30-1f179c2c6b06" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_33bf7583-8e0e-4b30-a8bb-e5c2308a2bac" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1_46fa66be-f99b-4479-ac30-1f179c2c6b06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1_a9b20b01-d741-48ea-a25a-5dd6443ecdf2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_33bf7583-8e0e-4b30-a8bb-e5c2308a2bac" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1_a9b20b01-d741-48ea-a25a-5dd6443ecdf2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLossesAndLossAdjustmentExpense_22d45873-7922-41e3-aae7-c4ba551d40bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsForLossesAndLossAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_33bf7583-8e0e-4b30-a8bb-e5c2308a2bac" xlink:to="loc_us-gaap_PaymentsForLossesAndLossAdjustmentExpense_22d45873-7922-41e3-aae7-c4ba551d40bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_IncreaseDecreaseInDeferredReinsuranceGain_44980b1c-108d-4440-8730-be1a7858329f" xlink:href="jrvr-20250331.xsd#jrvr_IncreaseDecreaseInDeferredReinsuranceGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:to="loc_jrvr_IncreaseDecreaseInDeferredReinsuranceGain_44980b1c-108d-4440-8730-be1a7858329f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_ad02a5fd-c817-456f-a53f-8fd089b8e0df" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesGross_8f67ecf0-4ec9-409a-bea3-1a2c03dd9bd5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReinsuranceRecoverablesOnUnpaidLossesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:to="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesGross_8f67ecf0-4ec9-409a-bea3-1a2c03dd9bd5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_6b4e3fcd-8fa1-45a6-b319-a3bff8fabc25" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_8c53f234-d6fb-48ae-89c6-517c993e1e4e" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_6b4e3fcd-8fa1-45a6-b319-a3bff8fabc25" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesRetroactiveReinsuranceDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#ReserveforLossesandLossAdjustmentExpensesRetroactiveReinsuranceDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesRetroactiveReinsuranceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_e9850930-3a4c-4b9b-b721-b00c43a8b8d2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_60a9253a-44af-4314-b771-f53f2d82bc95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_e9850930-3a4c-4b9b-b721-b00c43a8b8d2" xlink:to="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_60a9253a-44af-4314-b771-f53f2d82bc95" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_16c3f625-8d71-4c9d-b4f8-c5db689494cd" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_60a9253a-44af-4314-b771-f53f2d82bc95" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_16c3f625-8d71-4c9d-b4f8-c5db689494cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_16c3f625-8d71-4c9d-b4f8-c5db689494cd_default" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_16c3f625-8d71-4c9d-b4f8-c5db689494cd" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_16c3f625-8d71-4c9d-b4f8-c5db689494cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_727458fa-822f-4aca-8c66-8ee3af027ac0" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_16c3f625-8d71-4c9d-b4f8-c5db689494cd" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_727458fa-822f-4aca-8c66-8ee3af027ac0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoLPTAndESADCMember_00a7eec2-82a2-4ca7-a3e2-1e007e5bb15b" xlink:href="jrvr-20250331.xsd#jrvr_CommercialAutoLPTAndESADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_727458fa-822f-4aca-8c66-8ee3af027ac0" xlink:to="loc_jrvr_CommercialAutoLPTAndESADCMember_00a7eec2-82a2-4ca7-a3e2-1e007e5bb15b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LossPortfolioTransferMember_967693b1-7e3f-402a-8231-44b9c02d9db2" xlink:href="jrvr-20250331.xsd#jrvr_LossPortfolioTransferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_CommercialAutoLPTAndESADCMember_00a7eec2-82a2-4ca7-a3e2-1e007e5bb15b" xlink:to="loc_jrvr_LossPortfolioTransferMember_967693b1-7e3f-402a-8231-44b9c02d9db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ESADCAgreementMember_55743228-ef8c-4775-ab28-a78352fe4f66" xlink:href="jrvr-20250331.xsd#jrvr_ESADCAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_CommercialAutoLPTAndESADCMember_00a7eec2-82a2-4ca7-a3e2-1e007e5bb15b" xlink:to="loc_jrvr_ESADCAgreementMember_55743228-ef8c-4775-ab28-a78352fe4f66" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_f3b213dc-d505-4660-84a0-cb29c720bedc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_60a9253a-44af-4314-b771-f53f2d82bc95" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_f3b213dc-d505-4660-84a0-cb29c720bedc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_f3b213dc-d505-4660-84a0-cb29c720bedc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_f3b213dc-d505-4660-84a0-cb29c720bedc" xlink:to="loc_us-gaap_SegmentDomain_f3b213dc-d505-4660-84a0-cb29c720bedc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9e799420-8740-46b0-81d8-ffbce8375610" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_f3b213dc-d505-4660-84a0-cb29c720bedc" xlink:to="loc_us-gaap_SegmentDomain_9e799420-8740-46b0-81d8-ffbce8375610" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_3eb4c545-c3d1-417c-9313-740f6899997e" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9e799420-8740-46b0-81d8-ffbce8375610" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_3eb4c545-c3d1-417c-9313-740f6899997e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_d15206d4-46ea-492b-b49a-ec4e8303d826" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_60a9253a-44af-4314-b771-f53f2d82bc95" xlink:to="loc_us-gaap_SubsegmentsAxis_d15206d4-46ea-492b-b49a-ec4e8303d826" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_d15206d4-46ea-492b-b49a-ec4e8303d826_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_d15206d4-46ea-492b-b49a-ec4e8303d826" xlink:to="loc_us-gaap_SubsegmentsDomain_d15206d4-46ea-492b-b49a-ec4e8303d826_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_36e43d90-681d-4c6a-b596-0af6f197435c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_d15206d4-46ea-492b-b49a-ec4e8303d826" xlink:to="loc_us-gaap_SubsegmentsDomain_36e43d90-681d-4c6a-b596-0af6f197435c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoBusinessMember_f27b7c95-b50b-48b5-9b70-bb2d081647b9" xlink:href="jrvr-20250331.xsd#jrvr_CommercialAutoBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_36e43d90-681d-4c6a-b596-0af6f197435c" xlink:to="loc_jrvr_CommercialAutoBusinessMember_f27b7c95-b50b-48b5-9b70-bb2d081647b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DeferredReinsuranceGain_1dfe9122-cb84-4bd9-9931-9d74fb6dc273" xlink:href="jrvr-20250331.xsd#jrvr_DeferredReinsuranceGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_e9850930-3a4c-4b9b-b721-b00c43a8b8d2" xlink:to="loc_jrvr_DeferredReinsuranceGain_1dfe9122-cb84-4bd9-9931-9d74fb6dc273" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_c272203e-664b-4374-9c67-a660d1cfcbe3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_e9850930-3a4c-4b9b-b721-b00c43a8b8d2" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_c272203e-664b-4374-9c67-a660d1cfcbe3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RetroactiveReinsuranceBenefitRecognized_2f18ad78-a5c8-4759-9d1e-19a9da6bb286" xlink:href="jrvr-20250331.xsd#jrvr_RetroactiveReinsuranceBenefitRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_e9850930-3a4c-4b9b-b721-b00c43a8b8d2" xlink:to="loc_jrvr_RetroactiveReinsuranceBenefitRecognized_2f18ad78-a5c8-4759-9d1e-19a9da6bb286" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DeferredReinsuranceGain_90d87fef-5fcd-434e-843d-51e0996b1eea" xlink:href="jrvr-20250331.xsd#jrvr_DeferredReinsuranceGain"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ContingentLiabilitiesDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#ContingentLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/ContingentLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ContingentLiabilitiesLineItems_7d7afa2a-8f7a-4d17-9a8c-72859d5a05e8" xlink:href="jrvr-20250331.xsd#jrvr_ContingentLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ContingentLiabilitiesTable_b38765c0-4ce9-43df-9737-11ddbfade887" xlink:href="jrvr-20250331.xsd#jrvr_ContingentLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_7d7afa2a-8f7a-4d17-9a8c-72859d5a05e8" xlink:to="loc_jrvr_ContingentLiabilitiesTable_b38765c0-4ce9-43df-9737-11ddbfade887" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_57300193-9624-4b89-8e6d-b5cd6a6517ae" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_b38765c0-4ce9-43df-9737-11ddbfade887" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_57300193-9624-4b89-8e6d-b5cd6a6517ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_57300193-9624-4b89-8e6d-b5cd6a6517ae_default" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_57300193-9624-4b89-8e6d-b5cd6a6517ae" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_57300193-9624-4b89-8e6d-b5cd6a6517ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_4d839c3d-2c24-45ef-8f9d-39dff0593f4b" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_57300193-9624-4b89-8e6d-b5cd6a6517ae" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_4d839c3d-2c24-45ef-8f9d-39dff0593f4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LossPortfolioTransferMember_26633463-dd0c-43fe-8e30-59d0926f5394" xlink:href="jrvr-20250331.xsd#jrvr_LossPortfolioTransferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_4d839c3d-2c24-45ef-8f9d-39dff0593f4b" xlink:to="loc_jrvr_LossPortfolioTransferMember_26633463-dd0c-43fe-8e30-59d0926f5394" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_05494705-cb75-46b5-88d4-f3adeb6bc1dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_b38765c0-4ce9-43df-9737-11ddbfade887" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_05494705-cb75-46b5-88d4-f3adeb6bc1dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_05494705-cb75-46b5-88d4-f3adeb6bc1dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_05494705-cb75-46b5-88d4-f3adeb6bc1dc" xlink:to="loc_us-gaap_SegmentDomain_05494705-cb75-46b5-88d4-f3adeb6bc1dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_89bb50c4-4eed-4140-b51b-c74626b0720a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_05494705-cb75-46b5-88d4-f3adeb6bc1dc" xlink:to="loc_us-gaap_SegmentDomain_89bb50c4-4eed-4140-b51b-c74626b0720a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_bf03d39d-b7dd-461d-94c2-8179e4230116" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_89bb50c4-4eed-4140-b51b-c74626b0720a" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_bf03d39d-b7dd-461d-94c2-8179e4230116" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_1cf30d1b-989c-4dd8-8cec-1a2f4cc92528" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_b38765c0-4ce9-43df-9737-11ddbfade887" xlink:to="loc_us-gaap_SubsegmentsAxis_1cf30d1b-989c-4dd8-8cec-1a2f4cc92528" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_1cf30d1b-989c-4dd8-8cec-1a2f4cc92528_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_1cf30d1b-989c-4dd8-8cec-1a2f4cc92528" xlink:to="loc_us-gaap_SubsegmentsDomain_1cf30d1b-989c-4dd8-8cec-1a2f4cc92528_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_568fb8d8-8e96-4642-b236-0a6e62a8ca19" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_1cf30d1b-989c-4dd8-8cec-1a2f4cc92528" xlink:to="loc_us-gaap_SubsegmentsDomain_568fb8d8-8e96-4642-b236-0a6e62a8ca19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoBusinessMember_d1003cda-36ca-4a75-94eb-0bb7f4ad688a" xlink:href="jrvr-20250331.xsd#jrvr_CommercialAutoBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_568fb8d8-8e96-4642-b236-0a6e62a8ca19" xlink:to="loc_jrvr_CommercialAutoBusinessMember_d1003cda-36ca-4a75-94eb-0bb7f4ad688a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_0300d842-e77e-4b80-b952-145831662673" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_b38765c0-4ce9-43df-9737-11ddbfade887" xlink:to="loc_srt_CounterpartyNameAxis_0300d842-e77e-4b80-b952-145831662673" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0300d842-e77e-4b80-b952-145831662673_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_0300d842-e77e-4b80-b952-145831662673" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0300d842-e77e-4b80-b952-145831662673_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_a9c17fdf-7db2-479f-a1e1-a541ddd248af" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_0300d842-e77e-4b80-b952-145831662673" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_a9c17fdf-7db2-479f-a1e1-a541ddd248af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AlekaMember_dbe2f093-1d4a-44c4-ae20-5dca8a404776" xlink:href="jrvr-20250331.xsd#jrvr_AlekaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_a9c17fdf-7db2-479f-a1e1-a541ddd248af" xlink:to="loc_jrvr_AlekaMember_dbe2f093-1d4a-44c4-ae20-5dca8a404776" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RasierMember_cdc91231-c119-401c-9da3-71e3954d7cbc" xlink:href="jrvr-20250331.xsd#jrvr_RasierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_a9c17fdf-7db2-479f-a1e1-a541ddd248af" xlink:to="loc_jrvr_RasierMember_cdc91231-c119-401c-9da3-71e3954d7cbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RasierAndAlekaMember_8633754b-d349-4173-ae7c-12d40e78f6e9" xlink:href="jrvr-20250331.xsd#jrvr_RasierAndAlekaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_a9c17fdf-7db2-479f-a1e1-a541ddd248af" xlink:to="loc_jrvr_RasierAndAlekaMember_8633754b-d349-4173-ae7c-12d40e78f6e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssociatedTrustAgreementAxis_9aab9d92-b80c-432e-8a3d-e2d1a23d31a3" xlink:href="jrvr-20250331.xsd#jrvr_AssociatedTrustAgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_b38765c0-4ce9-43df-9737-11ddbfade887" xlink:to="loc_jrvr_AssociatedTrustAgreementAxis_9aab9d92-b80c-432e-8a3d-e2d1a23d31a3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssociatedTrustAgreementDomain_9aab9d92-b80c-432e-8a3d-e2d1a23d31a3_default" xlink:href="jrvr-20250331.xsd#jrvr_AssociatedTrustAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_AssociatedTrustAgreementAxis_9aab9d92-b80c-432e-8a3d-e2d1a23d31a3" xlink:to="loc_jrvr_AssociatedTrustAgreementDomain_9aab9d92-b80c-432e-8a3d-e2d1a23d31a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssociatedTrustAgreementDomain_face4cd0-0f7d-4d6d-b3a9-eb9826fb97f6" xlink:href="jrvr-20250331.xsd#jrvr_AssociatedTrustAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_AssociatedTrustAgreementAxis_9aab9d92-b80c-432e-8a3d-e2d1a23d31a3" xlink:to="loc_jrvr_AssociatedTrustAgreementDomain_face4cd0-0f7d-4d6d-b3a9-eb9826fb97f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_IndemnityTrustAndLossFundTrustMember_425975c5-6584-410c-944a-7bd1e45ce94d" xlink:href="jrvr-20250331.xsd#jrvr_IndemnityTrustAndLossFundTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AssociatedTrustAgreementDomain_face4cd0-0f7d-4d6d-b3a9-eb9826fb97f6" xlink:to="loc_jrvr_IndemnityTrustAndLossFundTrustMember_425975c5-6584-410c-944a-7bd1e45ce94d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LPTTrustAndLossFundTrustMember_42e896c1-b33c-4cfd-a7fa-5862ba1b7c24" xlink:href="jrvr-20250331.xsd#jrvr_LPTTrustAndLossFundTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AssociatedTrustAgreementDomain_face4cd0-0f7d-4d6d-b3a9-eb9826fb97f6" xlink:to="loc_jrvr_LPTTrustAndLossFundTrustMember_42e896c1-b33c-4cfd-a7fa-5862ba1b7c24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LossFundTrustMember_cd176086-410d-4018-8677-167d97c17acb" xlink:href="jrvr-20250331.xsd#jrvr_LossFundTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AssociatedTrustAgreementDomain_face4cd0-0f7d-4d6d-b3a9-eb9826fb97f6" xlink:to="loc_jrvr_LossFundTrustMember_cd176086-410d-4018-8677-167d97c17acb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_a1d71a13-7b01-4247-9c80-24cbc1c5e7fb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_7d7afa2a-8f7a-4d17-9a8c-72859d5a05e8" xlink:to="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_a1d71a13-7b01-4247-9c80-24cbc1c5e7fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RequiredCollateralPercentage_32f0e749-c687-4db2-9c53-c5899523e677" xlink:href="jrvr-20250331.xsd#jrvr_RequiredCollateralPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_7d7afa2a-8f7a-4d17-9a8c-72859d5a05e8" xlink:to="loc_jrvr_RequiredCollateralPercentage_32f0e749-c687-4db2-9c53-c5899523e677" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CashEquivalentCollateralHeldInTrustArrangement_df7606fc-dd46-4b0f-9266-15411ba4d81c" xlink:href="jrvr-20250331.xsd#jrvr_CashEquivalentCollateralHeldInTrustArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_7d7afa2a-8f7a-4d17-9a8c-72859d5a05e8" xlink:to="loc_jrvr_CashEquivalentCollateralHeldInTrustArrangement_df7606fc-dd46-4b0f-9266-15411ba4d81c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesGross_13bf1bbf-7199-42d5-bae4-3ce23c96a353" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReinsuranceRecoverablesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_7d7afa2a-8f7a-4d17-9a8c-72859d5a05e8" xlink:to="loc_us-gaap_ReinsuranceRecoverablesGross_13bf1bbf-7199-42d5-bae4-3ce23c96a353" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SegmentInformationScheduleofSegmentResultsDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#SegmentInformationScheduleofSegmentResultsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/SegmentInformationScheduleofSegmentResultsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bd29dbf0-f8e4-4c26-9308-adfd5d1a8d72" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bd29dbf0-f8e4-4c26-9308-adfd5d1a8d72" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_c05f8d99-7670-4c3e-9a75-f16615fa6100" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bd29dbf0-f8e4-4c26-9308-adfd5d1a8d72" xlink:to="loc_srt_ConsolidationItemsAxis_c05f8d99-7670-4c3e-9a75-f16615fa6100" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_c05f8d99-7670-4c3e-9a75-f16615fa6100_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_c05f8d99-7670-4c3e-9a75-f16615fa6100" xlink:to="loc_srt_ConsolidationItemsDomain_c05f8d99-7670-4c3e-9a75-f16615fa6100_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_8b0691e0-0cba-4b78-b20a-68c531aa1dff" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_c05f8d99-7670-4c3e-9a75-f16615fa6100" xlink:to="loc_srt_ConsolidationItemsDomain_8b0691e0-0cba-4b78-b20a-68c531aa1dff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_65342322-b720-4760-aacd-1d7ae3f56afc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_8b0691e0-0cba-4b78-b20a-68c531aa1dff" xlink:to="loc_us-gaap_OperatingSegmentsMember_65342322-b720-4760-aacd-1d7ae3f56afc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_c14295f2-df19-4669-a697-d89eab7f644b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_8b0691e0-0cba-4b78-b20a-68c531aa1dff" xlink:to="loc_us-gaap_CorporateNonSegmentMember_c14295f2-df19-4669-a697-d89eab7f644b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_e0c4528f-c01d-4174-a540-ad2a34c7e2e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_bd29dbf0-f8e4-4c26-9308-adfd5d1a8d72" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_e0c4528f-c01d-4174-a540-ad2a34c7e2e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_e0c4528f-c01d-4174-a540-ad2a34c7e2e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_e0c4528f-c01d-4174-a540-ad2a34c7e2e0" xlink:to="loc_us-gaap_SegmentDomain_e0c4528f-c01d-4174-a540-ad2a34c7e2e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8eafbeb6-6a93-4ddb-99e6-7bc470095ed3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_e0c4528f-c01d-4174-a540-ad2a34c7e2e0" xlink:to="loc_us-gaap_SegmentDomain_8eafbeb6-6a93-4ddb-99e6-7bc470095ed3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_5170ce50-78cd-4c4e-9849-7091ee741172" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8eafbeb6-6a93-4ddb-99e6-7bc470095ed3" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_5170ce50-78cd-4c4e-9849-7091ee741172" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SpecialtyAdmittedInsuranceMember_ac53d1cb-b699-4e14-be66-945310224938" xlink:href="jrvr-20250331.xsd#jrvr_SpecialtyAdmittedInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8eafbeb6-6a93-4ddb-99e6-7bc470095ed3" xlink:to="loc_jrvr_SpecialtyAdmittedInsuranceMember_ac53d1cb-b699-4e14-be66-945310224938" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_895e2391-5dff-4ce4-9cc7-fa3ac609b697" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8eafbeb6-6a93-4ddb-99e6-7bc470095ed3" xlink:to="loc_us-gaap_CorporateAndOtherMember_895e2391-5dff-4ce4-9cc7-fa3ac609b697" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsWrittenGross_6c9e78fb-527a-45ba-a72d-3b4de4ad3f40" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PremiumsWrittenGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_PremiumsWrittenGross_6c9e78fb-527a-45ba-a72d-3b4de4ad3f40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsEarnedNet_3d4935e6-9193-4b53-b543-6a30be13b580" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PremiumsEarnedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_PremiumsEarnedNet_3d4935e6-9193-4b53-b543-6a30be13b580" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FeeIncome_e5955d78-d290-44b2-8961-edf4484935a6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FeeIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_FeeIncome_e5955d78-d290-44b2-8961-edf4484935a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_848d029f-9b9b-4d48-9bc3-506c5615355f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_848d029f-9b9b-4d48-9bc3-506c5615355f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_95022b1b-6e0e-41fa-a8a3-10672226625c" xlink:href="jrvr-20250331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_95022b1b-6e0e-41fa-a8a3-10672226625c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseExcludingRetroactiveReinsurance_eed61e6c-7524-418a-b57a-e0ab437be741" xlink:href="jrvr-20250331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseExcludingRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseExcludingRetroactiveReinsurance_eed61e6c-7524-418a-b57a-e0ab437be741" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpensesAbstract_4107e0f6-bf98-4c10-921a-afd36cedfb29" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingCostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_OperatingCostsAndExpensesAbstract_4107e0f6-bf98-4c10-921a-afd36cedfb29" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceCommissions_7a412e64-7afc-422f-9be2-3a3281afa655" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InsuranceCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_4107e0f6-bf98-4c10-921a-afd36cedfb29" xlink:to="loc_us-gaap_InsuranceCommissions_7a412e64-7afc-422f-9be2-3a3281afa655" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_74e902c5-928d-41a1-b41f-bbffe21136d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_4107e0f6-bf98-4c10-921a-afd36cedfb29" xlink:to="loc_us-gaap_LaborAndRelatedExpense_74e902c5-928d-41a1-b41f-bbffe21136d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_OtherOperatingExpenses_32d8e2d9-ab2b-4f56-b438-d5d5ea90ccca" xlink:href="jrvr-20250331.xsd#jrvr_OtherOperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_4107e0f6-bf98-4c10-921a-afd36cedfb29" xlink:to="loc_jrvr_OtherOperatingExpenses_32d8e2d9-ab2b-4f56-b438-d5d5ea90ccca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_9bdbf4ce-2eaa-4f7f-9b61-58b419d70189" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_4107e0f6-bf98-4c10-921a-afd36cedfb29" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_9bdbf4ce-2eaa-4f7f-9b61-58b419d70189" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_UnderwritingProfitLoss_22d42714-72b4-40b9-9f40-487efdeab50a" xlink:href="jrvr-20250331.xsd#jrvr_UnderwritingProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_jrvr_UnderwritingProfitLoss_22d42714-72b4-40b9-9f40-487efdeab50a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_c5878b10-5ba0-4398-96f6-4b3a38b7b348" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_Revenues_c5878b10-5ba0-4398-96f6-4b3a38b7b348" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_c37be17c-ef4f-47ac-aaa1-b3364c79e995" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_NetInvestmentIncome_c37be17c-ef4f-47ac-aaa1-b3364c79e995" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_ab7eb132-30d2-4e57-8af1-90850ab4fc00" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_InterestExpense_ab7eb132-30d2-4e57-8af1-90850ab4fc00" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_fd9e37d9-e363-4636-899c-b96e25444a05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_us-gaap_Goodwill_fd9e37d9-e363-4636-899c-b96e25444a05" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssetsExcludingAssetsHeldForSale_57554213-2afe-45c4-9281-72266c1fc1bf" xlink:href="jrvr-20250331.xsd#jrvr_AssetsExcludingAssetsHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e741ed45-768a-476c-a3ef-f1c2e9252c6a" xlink:to="loc_jrvr_AssetsExcludingAssetsHeldForSale_57554213-2afe-45c4-9281-72266c1fc1bf" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SegmentInformationReconciliationofOperatingSegmentsbyIndividualSegmentDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#SegmentInformationReconciliationofOperatingSegmentsbyIndividualSegmentDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/SegmentInformationReconciliationofOperatingSegmentsbyIndividualSegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_69d3c181-e438-4568-ab8d-f7df6cdebb76" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_69d3c181-e438-4568-ab8d-f7df6cdebb76" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_f826ab28-1aa0-4d6a-b1f2-36823cf59f92" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_69d3c181-e438-4568-ab8d-f7df6cdebb76" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_f826ab28-1aa0-4d6a-b1f2-36823cf59f92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_f826ab28-1aa0-4d6a-b1f2-36823cf59f92_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_f826ab28-1aa0-4d6a-b1f2-36823cf59f92" xlink:to="loc_us-gaap_SegmentDomain_f826ab28-1aa0-4d6a-b1f2-36823cf59f92_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_1a0f276e-7d9e-4f4b-9885-5d0ffe045767" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_f826ab28-1aa0-4d6a-b1f2-36823cf59f92" xlink:to="loc_us-gaap_SegmentDomain_1a0f276e-7d9e-4f4b-9885-5d0ffe045767" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_2ffe43d4-2fd7-4ceb-bfba-0bc27c4fa643" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_1a0f276e-7d9e-4f4b-9885-5d0ffe045767" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_2ffe43d4-2fd7-4ceb-bfba-0bc27c4fa643" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SpecialtyAdmittedInsuranceMember_d0011a02-c66e-4287-810c-0900285fa389" xlink:href="jrvr-20250331.xsd#jrvr_SpecialtyAdmittedInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_1a0f276e-7d9e-4f4b-9885-5d0ffe045767" xlink:to="loc_jrvr_SpecialtyAdmittedInsuranceMember_d0011a02-c66e-4287-810c-0900285fa389" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_d2ef8bec-075c-4164-9700-7dc1138c1a48" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_69d3c181-e438-4568-ab8d-f7df6cdebb76" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_d2ef8bec-075c-4164-9700-7dc1138c1a48" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_d2ef8bec-075c-4164-9700-7dc1138c1a48_default" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_d2ef8bec-075c-4164-9700-7dc1138c1a48" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_d2ef8bec-075c-4164-9700-7dc1138c1a48_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_e7532724-5cb2-4de2-b998-b83edf211685" xlink:href="jrvr-20250331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_d2ef8bec-075c-4164-9700-7dc1138c1a48" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_e7532724-5cb2-4de2-b998-b83edf211685" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoLPTAndESADCMember_2c53dc33-d169-4a39-932c-4a6ffef5657d" xlink:href="jrvr-20250331.xsd#jrvr_CommercialAutoLPTAndESADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_e7532724-5cb2-4de2-b998-b83edf211685" xlink:to="loc_jrvr_CommercialAutoLPTAndESADCMember_2c53dc33-d169-4a39-932c-4a6ffef5657d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_UnderwritingProfitLossOfOperatingSegments_ab0e544a-55e0-4035-a9c5-9bd3ad494fc8" xlink:href="jrvr-20250331.xsd#jrvr_UnderwritingProfitLossOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_jrvr_UnderwritingProfitLossOfOperatingSegments_ab0e544a-55e0-4035-a9c5-9bd3ad494fc8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_OtherOperatingExpensesOfCorporateAndOtherSegment_1a762547-9dc1-4131-9dc7-cd4b8f98b2a2" xlink:href="jrvr-20250331.xsd#jrvr_OtherOperatingExpensesOfCorporateAndOtherSegment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_jrvr_OtherOperatingExpensesOfCorporateAndOtherSegment_1a762547-9dc1-4131-9dc7-cd4b8f98b2a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_UnderwritingProfitLoss_263cfab8-2ab6-4464-84f3-5228a3235d68" xlink:href="jrvr-20250331.xsd#jrvr_UnderwritingProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_jrvr_UnderwritingProfitLoss_263cfab8-2ab6-4464-84f3-5228a3235d68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_3ba48d79-1bde-4520-b4c7-6a2e108a730f" xlink:href="jrvr-20250331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_3ba48d79-1bde-4520-b4c7-6a2e108a730f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_91899e9c-2366-4665-9ffd-562efb3b16d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_us-gaap_NetInvestmentIncome_91899e9c-2366-4665-9ffd-562efb3b16d6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_05de7496-13c1-4742-92cd-f2eac1708eab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_us-gaap_GainLossOnInvestments_05de7496-13c1-4742-92cd-f2eac1708eab" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_OtherIncomeAndExpenses_7c16521b-5764-4f15-8ac9-100d7d32eac5" xlink:href="jrvr-20250331.xsd#jrvr_OtherIncomeAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_jrvr_OtherIncomeAndExpenses_7c16521b-5764-4f15-8ac9-100d7d32eac5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_f833249e-9bb9-41bf-871a-e4223ed37372" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_us-gaap_InterestExpense_f833249e-9bb9-41bf-871a-e4223ed37372" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_a3230b3c-e011-4dc2-a4d7-8c1771b3e852" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_a3230b3c-e011-4dc2-a4d7-8c1771b3e852" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_2d28ae04-566e-471f-8eef-e91dc023a05e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_8cf33927-10b4-40f1-b73f-8448ba1b1ef3" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_2d28ae04-566e-471f-8eef-e91dc023a05e" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SeniorDebtDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#SeniorDebtDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/SeniorDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_9c6f0883-4404-4275-951c-022f53bf213d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_b13f0f93-ed93-4363-9854-fb47eb3741c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9c6f0883-4404-4275-951c-022f53bf213d" xlink:to="loc_us-gaap_DebtInstrumentTable_b13f0f93-ed93-4363-9854-fb47eb3741c6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_5533639e-4215-4d33-82fb-eeb7ce5de77a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b13f0f93-ed93-4363-9854-fb47eb3741c6" xlink:to="loc_us-gaap_CreditFacilityAxis_5533639e-4215-4d33-82fb-eeb7ce5de77a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5533639e-4215-4d33-82fb-eeb7ce5de77a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_5533639e-4215-4d33-82fb-eeb7ce5de77a" xlink:to="loc_us-gaap_CreditFacilityDomain_5533639e-4215-4d33-82fb-eeb7ce5de77a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ad56b0cf-c0c7-4400-9a28-5a4ca46f813e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_5533639e-4215-4d33-82fb-eeb7ce5de77a" xlink:to="loc_us-gaap_CreditFacilityDomain_ad56b0cf-c0c7-4400-9a28-5a4ca46f813e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_A2013FacilityMember_018ba507-a057-4da1-847c-816758dc8937" xlink:href="jrvr-20250331.xsd#jrvr_A2013FacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_ad56b0cf-c0c7-4400-9a28-5a4ca46f813e" xlink:to="loc_jrvr_A2013FacilityMember_018ba507-a057-4da1-847c-816758dc8937" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_04a9b563-32eb-4ee4-95fe-7a16141116a6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b13f0f93-ed93-4363-9854-fb47eb3741c6" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_04a9b563-32eb-4ee4-95fe-7a16141116a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_04a9b563-32eb-4ee4-95fe-7a16141116a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_04a9b563-32eb-4ee4-95fe-7a16141116a6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_04a9b563-32eb-4ee4-95fe-7a16141116a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_34568630-cda8-45cb-9118-32ab04a5d615" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_04a9b563-32eb-4ee4-95fe-7a16141116a6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_34568630-cda8-45cb-9118-32ab04a5d615" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_999d6f86-eab3-4ec7-aed2-d09ea3f3ff10" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_34568630-cda8-45cb-9118-32ab04a5d615" xlink:to="loc_us-gaap_UnsecuredDebtMember_999d6f86-eab3-4ec7-aed2-d09ea3f3ff10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_b0f2a4b4-cc9d-4d5a-90a1-d03e3ce1aa7f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_34568630-cda8-45cb-9118-32ab04a5d615" xlink:to="loc_us-gaap_SecuredDebtMember_b0f2a4b4-cc9d-4d5a-90a1-d03e3ce1aa7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_2991aafa-c985-42d2-af34-22670ad6365d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9c6f0883-4404-4275-951c-022f53bf213d" xlink:to="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_2991aafa-c985-42d2-af34-22670ad6365d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_851eb92c-f1b5-43b1-9f66-c64a67a8ead7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9c6f0883-4404-4275-951c-022f53bf213d" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_851eb92c-f1b5-43b1-9f66-c64a67a8ead7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1610da7d-b6bc-4797-8deb-0157ef12d90a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9c6f0883-4404-4275-951c-022f53bf213d" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1610da7d-b6bc-4797-8deb-0157ef12d90a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_4ba927e8-0f22-46db-9367-ba29c6d9e6a5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9c6f0883-4404-4275-951c-022f53bf213d" xlink:to="loc_us-gaap_LineOfCredit_4ba927e8-0f22-46db-9367-ba29c6d9e6a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_28ebd728-5598-4080-b32d-869d8d5cc8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9c6f0883-4404-4275-951c-022f53bf213d" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_28ebd728-5598-4080-b32d-869d8d5cc8c3" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/FairValueMeasurementsScheduleofAssetsFairValueonaRecurringBasisDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#FairValueMeasurementsScheduleofAssetsFairValueonaRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/FairValueMeasurementsScheduleofAssetsFairValueonaRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b3581e59-29b1-4963-90d3-ce4c44272921" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_413248dd-aeb8-4cfe-981f-a3968b74cc59" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b3581e59-29b1-4963-90d3-ce4c44272921" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_413248dd-aeb8-4cfe-981f-a3968b74cc59" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_91503021-91c5-490a-9426-daca46721d73" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_413248dd-aeb8-4cfe-981f-a3968b74cc59" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_91503021-91c5-490a-9426-daca46721d73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_91503021-91c5-490a-9426-daca46721d73_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_91503021-91c5-490a-9426-daca46721d73" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_91503021-91c5-490a-9426-daca46721d73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_53aa224a-19e3-455f-b9f4-33cc4efb7461" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_91503021-91c5-490a-9426-daca46721d73" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_53aa224a-19e3-455f-b9f4-33cc4efb7461" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_2f4cc066-8b50-4575-8a94-4e58204c33a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_53aa224a-19e3-455f-b9f4-33cc4efb7461" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_2f4cc066-8b50-4575-8a94-4e58204c33a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3830f48b-5edf-493b-a1f1-41f3206919e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_413248dd-aeb8-4cfe-981f-a3968b74cc59" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3830f48b-5edf-493b-a1f1-41f3206919e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3830f48b-5edf-493b-a1f1-41f3206919e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3830f48b-5edf-493b-a1f1-41f3206919e9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3830f48b-5edf-493b-a1f1-41f3206919e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_61c20e8d-057f-4fa2-a018-60532c8b599f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3830f48b-5edf-493b-a1f1-41f3206919e9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_61c20e8d-057f-4fa2-a018-60532c8b599f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_a63b4d7e-92ef-4a3c-9e8e-23f1791a96c4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_61c20e8d-057f-4fa2-a018-60532c8b599f" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_a63b4d7e-92ef-4a3c-9e8e-23f1791a96c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_ba752d78-0668-470d-a9e9-cd67e68cf2f7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_61c20e8d-057f-4fa2-a018-60532c8b599f" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_ba752d78-0668-470d-a9e9-cd67e68cf2f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_d69b225d-2458-412f-a4f7-6561955275b6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_61c20e8d-057f-4fa2-a018-60532c8b599f" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_d69b225d-2458-412f-a4f7-6561955275b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_74c62c64-a2a8-4cb3-bbb3-96f35ade8bdf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_413248dd-aeb8-4cfe-981f-a3968b74cc59" xlink:to="loc_us-gaap_FinancialInstrumentAxis_74c62c64-a2a8-4cb3-bbb3-96f35ade8bdf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_74c62c64-a2a8-4cb3-bbb3-96f35ade8bdf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_74c62c64-a2a8-4cb3-bbb3-96f35ade8bdf" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_74c62c64-a2a8-4cb3-bbb3-96f35ade8bdf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_14c78a93-7797-4c0c-bb63-73548a7d9e74" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_74c62c64-a2a8-4cb3-bbb3-96f35ade8bdf" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_14c78a93-7797-4c0c-bb63-73548a7d9e74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_73abc40e-a944-4416-9609-88076373b6d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_14c78a93-7797-4c0c-bb63-73548a7d9e74" xlink:to="loc_us-gaap_DebtSecuritiesMember_73abc40e-a944-4416-9609-88076373b6d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_c7f29856-4cf7-48fe-8eb4-34658f0e65cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_73abc40e-a944-4416-9609-88076373b6d0" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_c7f29856-4cf7-48fe-8eb4-34658f0e65cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_b496c4c8-f11a-4e05-b21c-7bc98a28c8d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_73abc40e-a944-4416-9609-88076373b6d0" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_b496c4c8-f11a-4e05-b21c-7bc98a28c8d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_79b07010-b139-4d7e-bd8b-264c7e79ed8b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_73abc40e-a944-4416-9609-88076373b6d0" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_79b07010-b139-4d7e-bd8b-264c7e79ed8b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_450b98d1-21dc-4b3a-9d1a-85f3a44b36db" xlink:href="jrvr-20250331.xsd#jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_73abc40e-a944-4416-9609-88076373b6d0" xlink:to="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_450b98d1-21dc-4b3a-9d1a-85f3a44b36db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_819066c2-81f0-4849-b08e-7741898d2efe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_73abc40e-a944-4416-9609-88076373b6d0" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_819066c2-81f0-4849-b08e-7741898d2efe" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_6facacdd-620d-46f9-bc74-47671535a157" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_14c78a93-7797-4c0c-bb63-73548a7d9e74" xlink:to="loc_us-gaap_EquitySecuritiesMember_6facacdd-620d-46f9-bc74-47671535a157" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_4a9e411e-4a54-4b3c-85d5-fbef285f7223" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesMember_6facacdd-620d-46f9-bc74-47671535a157" xlink:to="loc_us-gaap_PreferredStockMember_4a9e411e-4a54-4b3c-85d5-fbef285f7223" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_a7531f0e-7933-42c9-b42a-f529dce60841" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesMember_6facacdd-620d-46f9-bc74-47671535a157" xlink:to="loc_us-gaap_CommonStockMember_a7531f0e-7933-42c9-b42a-f529dce60841" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAbstract_00e90d32-7584-494c-acde-ef7262ac188b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b3581e59-29b1-4963-90d3-ce4c44272921" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAbstract_00e90d32-7584-494c-acde-ef7262ac188b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0e340644-a686-4f5a-8612-2700465377b6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_00e90d32-7584-494c-acde-ef7262ac188b" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0e340644-a686-4f5a-8612-2700465377b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsAbstract_fb470611-e9ec-467f-90e9-8016a42333fe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermInvestmentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b3581e59-29b1-4963-90d3-ce4c44272921" xlink:to="loc_us-gaap_ShortTermInvestmentsAbstract_fb470611-e9ec-467f-90e9-8016a42333fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_434dacc5-d761-4b60-8293-bfc58c2b6b4d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermInvestmentsAbstract_fb470611-e9ec-467f-90e9-8016a42333fe" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_434dacc5-d761-4b60-8293-bfc58c2b6b4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_ed2f38c6-776f-4dfe-912a-424a4c9e5610" xlink:href="jrvr-20250331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b3581e59-29b1-4963-90d3-ce4c44272921" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_ed2f38c6-776f-4dfe-912a-424a4c9e5610" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherShortTermInvestments_1bcf2e4c-ed60-4d99-b477-1109c8a375a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b3581e59-29b1-4963-90d3-ce4c44272921" xlink:to="loc_us-gaap_OtherShortTermInvestments_1bcf2e4c-ed60-4d99-b477-1109c8a375a7" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/FairValueMeasurementsScheduleofAvailableforSaleFixedMaturitySecuritiesMeasuredatFairValueonaRecurringBasisDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#FairValueMeasurementsScheduleofAvailableforSaleFixedMaturitySecuritiesMeasuredatFairValueonaRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/FairValueMeasurementsScheduleofAvailableforSaleFixedMaturitySecuritiesMeasuredatFairValueonaRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_694a3c5e-da99-445d-9e46-9960bd4750a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9c80f3be-4ea3-4eae-8427-e4a715244e9f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_694a3c5e-da99-445d-9e46-9960bd4750a4" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9c80f3be-4ea3-4eae-8427-e4a715244e9f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_d2be0587-e25e-4ff0-89b3-747d14ffed9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9c80f3be-4ea3-4eae-8427-e4a715244e9f" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_d2be0587-e25e-4ff0-89b3-747d14ffed9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_d2be0587-e25e-4ff0-89b3-747d14ffed9e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_d2be0587-e25e-4ff0-89b3-747d14ffed9e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_d2be0587-e25e-4ff0-89b3-747d14ffed9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_c97385e3-0478-478a-a29a-cc56e4e7dfd2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_d2be0587-e25e-4ff0-89b3-747d14ffed9e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_c97385e3-0478-478a-a29a-cc56e4e7dfd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_c9d4103e-fb74-4b53-b883-2d9f82d67d62" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_c97385e3-0478-478a-a29a-cc56e4e7dfd2" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_c9d4103e-fb74-4b53-b883-2d9f82d67d62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_cb2482cb-0373-4b40-a66c-2a279d7f607f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9c80f3be-4ea3-4eae-8427-e4a715244e9f" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_cb2482cb-0373-4b40-a66c-2a279d7f607f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_cb2482cb-0373-4b40-a66c-2a279d7f607f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_cb2482cb-0373-4b40-a66c-2a279d7f607f" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_cb2482cb-0373-4b40-a66c-2a279d7f607f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9f151ecf-b729-45cc-8d74-34c1d0fb7c86" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_cb2482cb-0373-4b40-a66c-2a279d7f607f" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9f151ecf-b729-45cc-8d74-34c1d0fb7c86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesAssetsMember_026b28a5-ac80-4bcf-a49c-4c6a3a19b409" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuritiesAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_9f151ecf-b729-45cc-8d74-34c1d0fb7c86" xlink:to="loc_us-gaap_SecuritiesAssetsMember_026b28a5-ac80-4bcf-a49c-4c6a3a19b409" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_694a3c5e-da99-445d-9e46-9960bd4750a4" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_cc4a562e-65e3-47af-8853-6b1d516a5774" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_cc4a562e-65e3-47af-8853-6b1d516a5774" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_25b9f09a-97bb-49c9-8583-c7e1be0837f5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_25b9f09a-97bb-49c9-8583-c7e1be0837f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_c875d356-cba8-438c-ab90-e888ee6985cf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_c875d356-cba8-438c-ab90-e888ee6985cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_0499c8d9-2838-43a5-a396-1975f7106926" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_0499c8d9-2838-43a5-a396-1975f7106926" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_eb93d984-ba72-413f-a101-5030e810edde" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_eb93d984-ba72-413f-a101-5030e810edde" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_cc37da66-b034-49e2-98c6-4275e773354a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_cc37da66-b034-49e2-98c6-4275e773354a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetAmortizationofDiscount_bc8c7a99-4908-403d-b9fd-4012b9b1437a" xlink:href="jrvr-20250331.xsd#jrvr_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetAmortizationofDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_jrvr_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetAmortizationofDiscount_bc8c7a99-4908-403d-b9fd-4012b9b1437a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_821a26f4-b603-4fd7-bf2d-3ee710ec0bb1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_821a26f4-b603-4fd7-bf2d-3ee710ec0bb1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_76a643e1-e712-4820-942d-083d6195ee95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_f28e83df-56e7-4ce5-9320-756c5329c09a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_76a643e1-e712-4820-942d-083d6195ee95" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_a424570e-7c3f-4274-ad85-601d1d345fab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/FairValueMeasurementsNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#FairValueMeasurementsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/FairValueMeasurementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_a4c57580-9d5d-432a-b7fe-cc49056be30e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_1e5810fd-0b4f-4e2c-a9c1-30696162fab8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_a4c57580-9d5d-432a-b7fe-cc49056be30e" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_1e5810fd-0b4f-4e2c-a9c1-30696162fab8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3f494709-8d35-4c00-9618-c186cba05606" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_1e5810fd-0b4f-4e2c-a9c1-30696162fab8" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3f494709-8d35-4c00-9618-c186cba05606" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_3f494709-8d35-4c00-9618-c186cba05606_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3f494709-8d35-4c00-9618-c186cba05606" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_3f494709-8d35-4c00-9618-c186cba05606_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_fd886460-e4ce-42a2-a8dc-78dba026cec2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_3f494709-8d35-4c00-9618-c186cba05606" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_fd886460-e4ce-42a2-a8dc-78dba026cec2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_8d8dd788-39b5-4fae-ab3e-f37462b49e11" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_fd886460-e4ce-42a2-a8dc-78dba026cec2" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_8d8dd788-39b5-4fae-ab3e-f37462b49e11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_2697ab26-61b8-4b39-a96b-bf1840dca17d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_1e5810fd-0b4f-4e2c-a9c1-30696162fab8" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_2697ab26-61b8-4b39-a96b-bf1840dca17d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2697ab26-61b8-4b39-a96b-bf1840dca17d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_2697ab26-61b8-4b39-a96b-bf1840dca17d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2697ab26-61b8-4b39-a96b-bf1840dca17d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a6911adf-ad54-458b-817b-f1302e65f186" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_2697ab26-61b8-4b39-a96b-bf1840dca17d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a6911adf-ad54-458b-817b-f1302e65f186" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesAssetsMember_09d7d6ce-09b7-4e7c-8af1-793938048337" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuritiesAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a6911adf-ad54-458b-817b-f1302e65f186" xlink:to="loc_us-gaap_SecuritiesAssetsMember_09d7d6ce-09b7-4e7c-8af1-793938048337" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfEquitySecuritiesHeld_ebd96890-8923-462e-a3f4-eb739333b859" xlink:href="jrvr-20250331.xsd#jrvr_NumberOfEquitySecuritiesHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_a4c57580-9d5d-432a-b7fe-cc49056be30e" xlink:to="loc_jrvr_NumberOfEquitySecuritiesHeld_ebd96890-8923-462e-a3f4-eb739333b859" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_7c8229e7-f0b4-4836-89b1-be418be79f30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_a4c57580-9d5d-432a-b7fe-cc49056be30e" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_7c8229e7-f0b4-4836-89b1-be418be79f30" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/FairValueMeasurementsScheduleoftheCarryingValueandFairValuesofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#FairValueMeasurementsScheduleoftheCarryingValueandFairValuesofFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/FairValueMeasurementsScheduleoftheCarryingValueandFairValuesofFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_2752e592-0e50-49fd-ad87-6c0727864cc8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_9f4b3f6b-22be-4a8f-9879-3504d44323b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_2752e592-0e50-49fd-ad87-6c0727864cc8" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_9f4b3f6b-22be-4a8f-9879-3504d44323b1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_57e3d455-c157-4dae-9b9d-c0df9edfe9e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_9f4b3f6b-22be-4a8f-9879-3504d44323b1" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_57e3d455-c157-4dae-9b9d-c0df9edfe9e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_57e3d455-c157-4dae-9b9d-c0df9edfe9e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_57e3d455-c157-4dae-9b9d-c0df9edfe9e5" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_57e3d455-c157-4dae-9b9d-c0df9edfe9e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_20128379-cb39-4130-a6a3-940587063be4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_57e3d455-c157-4dae-9b9d-c0df9edfe9e5" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_20128379-cb39-4130-a6a3-940587063be4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_08bd2aeb-502e-4173-823b-effdfd617983" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_20128379-cb39-4130-a6a3-940587063be4" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_08bd2aeb-502e-4173-823b-effdfd617983" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_96c0a784-10d9-48e0-bea0-21e8189b1324" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_08bd2aeb-502e-4173-823b-effdfd617983" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_96c0a784-10d9-48e0-bea0-21e8189b1324" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_2e2dcf37-8cfd-431e-a770-6dc96b982656" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_08bd2aeb-502e-4173-823b-effdfd617983" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_2e2dcf37-8cfd-431e-a770-6dc96b982656" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_2752e592-0e50-49fd-ad87-6c0727864cc8" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_54ffc5b2-2a43-4f68-a6f3-d0bb80ad0825" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_54ffc5b2-2a43-4f68-a6f3-d0bb80ad0825" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_aec314e8-cfc5-46f5-bf7d-dff15fc7118b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_aec314e8-cfc5-46f5-bf7d-dff15fc7118b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_3c73075e-6dd5-4a71-b806-583a5ce4799a" xlink:href="jrvr-20250331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_3c73075e-6dd5-4a71-b806-583a5ce4799a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_38b864ec-a17c-4bec-92cd-8b6e1129c94b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_38b864ec-a17c-4bec-92cd-8b6e1129c94b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashEquivalents_014324da-614b-4843-b395-1087b4b90dce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:to="loc_us-gaap_RestrictedCashEquivalents_014324da-614b-4843-b395-1087b4b90dce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherShortTermInvestments_db86193e-aecf-4fb9-9a5a-576329b1df53" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:to="loc_us-gaap_OtherShortTermInvestments_db86193e-aecf-4fb9-9a5a-576329b1df53" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivable_6d1d63af-475a-4ae3-bf31-290dc738e836" xlink:href="jrvr-20250331.xsd#jrvr_NotesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_b3e0c2e9-bd2d-43d9-9e47-2a826326aa69" xlink:to="loc_jrvr_NotesReceivable_6d1d63af-475a-4ae3-bf31-290dc738e836" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_6fe72e57-da30-47d1-9b7d-2cd65c3b0777" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_2752e592-0e50-49fd-ad87-6c0727864cc8" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_6fe72e57-da30-47d1-9b7d-2cd65c3b0777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_456862e3-bbf0-466f-9218-a5ab1ab97867" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_6fe72e57-da30-47d1-9b7d-2cd65c3b0777" xlink:to="loc_us-gaap_LineOfCredit_456862e3-bbf0-466f-9218-a5ab1ab97867" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_1eeca822-3e6a-45f6-a357-4c53d311b93b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_6fe72e57-da30-47d1-9b7d-2cd65c3b0777" xlink:to="loc_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_1eeca822-3e6a-45f6-a357-4c53d311b93b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SeriesAPreferredSharesDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#SeriesAPreferredSharesDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/SeriesAPreferredSharesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_796108b7-2440-463a-a2cd-22f55ac98c68" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_796108b7-2440-463a-a2cd-22f55ac98c68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_9c476fee-c844-4488-bb35-ea85ca8ad547" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_796108b7-2440-463a-a2cd-22f55ac98c68" xlink:to="loc_us-gaap_StatementClassOfStockAxis_9c476fee-c844-4488-bb35-ea85ca8ad547" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9c476fee-c844-4488-bb35-ea85ca8ad547_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9c476fee-c844-4488-bb35-ea85ca8ad547" xlink:to="loc_us-gaap_ClassOfStockDomain_9c476fee-c844-4488-bb35-ea85ca8ad547_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5bcc84a7-b4e9-49b3-a6b5-47c35a6620ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9c476fee-c844-4488-bb35-ea85ca8ad547" xlink:to="loc_us-gaap_ClassOfStockDomain_5bcc84a7-b4e9-49b3-a6b5-47c35a6620ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_950e915c-c3f6-4be4-b7f4-73b151b4846a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5bcc84a7-b4e9-49b3-a6b5-47c35a6620ee" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_950e915c-c3f6-4be4-b7f4-73b151b4846a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_7cab047c-861d-489e-9047-0454efd8eaea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_796108b7-2440-463a-a2cd-22f55ac98c68" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_7cab047c-861d-489e-9047-0454efd8eaea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7cab047c-861d-489e-9047-0454efd8eaea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_7cab047c-861d-489e-9047-0454efd8eaea" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7cab047c-861d-489e-9047-0454efd8eaea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_29d3cdbd-49cb-41e6-816b-4dbc990970aa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_7cab047c-861d-489e-9047-0454efd8eaea" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_29d3cdbd-49cb-41e6-816b-4dbc990970aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_e1f6ff1c-d7a3-4fb6-9594-dab8b837e923" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_29d3cdbd-49cb-41e6-816b-4dbc990970aa" xlink:to="loc_us-gaap_PrivatePlacementMember_e1f6ff1c-d7a3-4fb6-9594-dab8b837e923" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_c8a89ee5-fb76-4ace-bccf-111a4ec7fa97" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_796108b7-2440-463a-a2cd-22f55ac98c68" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_c8a89ee5-fb76-4ace-bccf-111a4ec7fa97" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_c8a89ee5-fb76-4ace-bccf-111a4ec7fa97_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c8a89ee5-fb76-4ace-bccf-111a4ec7fa97" xlink:to="loc_us-gaap_EquityComponentDomain_c8a89ee5-fb76-4ace-bccf-111a4ec7fa97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_e7501775-9320-42c0-9fb4-13123764f713" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c8a89ee5-fb76-4ace-bccf-111a4ec7fa97" xlink:to="loc_us-gaap_EquityComponentDomain_e7501775-9320-42c0-9fb4-13123764f713" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_32a7f2b2-54be-4ebc-879c-36f2ed84a703" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_e7501775-9320-42c0-9fb4-13123764f713" xlink:to="loc_us-gaap_CommonStockMember_32a7f2b2-54be-4ebc-879c-36f2ed84a703" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_d2e612e3-1012-446d-9d17-20aea0ef8ad2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_e7501775-9320-42c0-9fb4-13123764f713" xlink:to="loc_us-gaap_RetainedEarningsMember_d2e612e3-1012-446d-9d17-20aea0ef8ad2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingAMBestAxis_c8ae1918-a4b0-4454-82d4-200334fe2e24" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CreditRatingAMBestAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_796108b7-2440-463a-a2cd-22f55ac98c68" xlink:to="loc_srt_CreditRatingAMBestAxis_c8ae1918-a4b0-4454-82d4-200334fe2e24" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingAMBestDomain_c8ae1918-a4b0-4454-82d4-200334fe2e24_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CreditRatingAMBestDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CreditRatingAMBestAxis_c8ae1918-a4b0-4454-82d4-200334fe2e24" xlink:to="loc_srt_CreditRatingAMBestDomain_c8ae1918-a4b0-4454-82d4-200334fe2e24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingAMBestDomain_c4b3fa83-bb26-47a8-b74e-8a8f19a55e52" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CreditRatingAMBestDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CreditRatingAMBestAxis_c8ae1918-a4b0-4454-82d4-200334fe2e24" xlink:to="loc_srt_CreditRatingAMBestDomain_c4b3fa83-bb26-47a8-b74e-8a8f19a55e52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AMBestBelowARatingMember_58ab519c-f0d7-4f20-a396-85d83bd3d7a1" xlink:href="jrvr-20250331.xsd#jrvr_AMBestBelowARatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CreditRatingAMBestDomain_c4b3fa83-bb26-47a8-b74e-8a8f19a55e52" xlink:to="loc_jrvr_AMBestBelowARatingMember_58ab519c-f0d7-4f20-a396-85d83bd3d7a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_b6e7dd4b-5857-44ff-bb08-8815d6885d44" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_b6e7dd4b-5857-44ff-bb08-8815d6885d44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendRatePercentage_4995d3e0-e222-4420-b9d3-2f4738f95b8c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockDividendRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_PreferredStockDividendRatePercentage_4995d3e0-e222-4420-b9d3-2f4738f95b8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_5327a2c1-dd47-4d85-b98a-4e0737e6c611" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_5327a2c1-dd47-4d85-b98a-4e0737e6c611" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_ebd18435-3260-4da4-940b-495f65c98da4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_ebd18435-3260-4da4-940b-495f65c98da4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_07f7f422-aa2f-4014-8936-2cf9a0c97b4d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_07f7f422-aa2f-4014-8936-2cf9a0c97b4d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_2faae0eb-28f1-4dab-b9bd-f4eda297a28f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityLiquidationPreferencePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_2faae0eb-28f1-4dab-b9bd-f4eda297a28f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDividendTerm_de751af1-87ff-430b-86af-43ebabec1658" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockDividendTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockDividendTerm_de751af1-87ff-430b-86af-43ebabec1658" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDividendPaymentRateVariableSpread_bbc2cae9-80f5-4a9b-af51-d8644eb53db2" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockDividendPaymentRateVariableSpread"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockDividendPaymentRateVariableSpread_bbc2cae9-80f5-4a9b-af51-d8644eb53db2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock_d4407ed7-bcda-449e-b695-a155ecd65cd0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock_d4407ed7-bcda-449e-b695-a155ecd65cd0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionPrice_c375fec5-84d0-48fa-88e3-d7e3eb171a2b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockConvertibleConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionPrice_c375fec5-84d0-48fa-88e3-d7e3eb171a2b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_9edee6b6-b614-4da0-8e64-6a1357cd0f95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_9edee6b6-b614-4da0-8e64-6a1357cd0f95" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleFloorConversionPrice_9f5bf8a7-f929-409d-8b3c-bc146260f7e4" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockConvertibleFloorConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockConvertibleFloorConversionPrice_9f5bf8a7-f929-409d-8b3c-bc146260f7e4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommonStockCovenantThresholdPerShare_ad0894ed-ce2c-45c3-84c7-e6e196258012" xlink:href="jrvr-20250331.xsd#jrvr_CommonStockCovenantThresholdPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_CommonStockCovenantThresholdPerShare_ad0894ed-ce2c-45c3-84c7-e6e196258012" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommonStockDividendPerShareCashPaymentsThreshold_7eeeadb3-f2e4-4cb9-91c4-64f2b1f91529" xlink:href="jrvr-20250331.xsd#jrvr_CommonStockDividendPerShareCashPaymentsThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_CommonStockDividendPerShareCashPaymentsThreshold_7eeeadb3-f2e4-4cb9-91c4-64f2b1f91529" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleTerm_09bdd4a8-59af-42cb-bb0b-028599ba4b00" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockConvertibleTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockConvertibleTerm_09bdd4a8-59af-42cb-bb0b-028599ba4b00" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleMandatoryConversionPercentage_5317bdeb-3695-4018-b745-1607b0d8f9aa" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockConvertibleMandatoryConversionPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockConvertibleMandatoryConversionPercentage_5317bdeb-3695-4018-b745-1607b0d8f9aa" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleNumberOfTradingDays_059bc327-7da7-4124-b2e4-bfb18cb8c6d1" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockConvertibleNumberOfTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockConvertibleNumberOfTradingDays_059bc327-7da7-4124-b2e4-bfb18cb8c6d1" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDiscountRatePercentage_d5c3c90e-5957-4ebd-a373-06e91f565904" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockDiscountRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockDiscountRatePercentage_d5c3c90e-5957-4ebd-a373-06e91f565904" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDividendTradingDays_18a65b63-8314-419d-bca8-9ed48de515f6" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockDividendTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockDividendTradingDays_18a65b63-8314-419d-bca8-9ed48de515f6" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_63f6647b-4d22-41d3-944d-4d28fa86c067" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_63f6647b-4d22-41d3-944d-4d28fa86c067" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock_d31dfe2f-86d0-47d7-ad95-214d9dc05dac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock_d31dfe2f-86d0-47d7-ad95-214d9dc05dac" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_7382d670-0394-42d5-b5c0-cc103e97eeba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_7382d670-0394-42d5-b5c0-cc103e97eeba" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleVoluntaryConversionPercentage_291b3454-a282-43bd-8850-0be25b16cc6c" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockConvertibleVoluntaryConversionPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockConvertibleVoluntaryConversionPercentage_291b3454-a282-43bd-8850-0be25b16cc6c" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleVotingEquityMaximum_d52efe0f-481e-4613-adb0-f889efbfb6cf" xlink:href="jrvr-20250331.xsd#jrvr_PreferredStockConvertibleVotingEquityMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_PreferredStockConvertibleVotingEquityMaximum_d52efe0f-481e-4613-adb0-f889efbfb6cf" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_e9381265-bc93-4104-bf29-c3cc04bd4c7b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_PreferredStockValue_e9381265-bc93-4104-bf29-c3cc04bd4c7b" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExtinguishmentOfPreferredStockDeemedDividend_107a69c2-2fb4-45c9-9f26-da3467107358" xlink:href="jrvr-20250331.xsd#jrvr_ExtinguishmentOfPreferredStockDeemedDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_jrvr_ExtinguishmentOfPreferredStockDeemedDividend_107a69c2-2fb4-45c9-9f26-da3467107358" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_eed2e652-f9e6-464a-a96d-457f5ffc9a99" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_8d0476bc-3940-4725-bf11-5614ee68b278" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_eed2e652-f9e6-464a-a96d-457f5ffc9a99" xlink:type="arc" order="26"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsCommonSharesDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#CapitalStockandEquityAwardsCommonSharesDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/CapitalStockandEquityAwardsCommonSharesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_14227d1d-28b6-4678-9c82-a226d3dbfd16" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15c7eea0-4b16-4edb-9e14-116e260f7cc7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_14227d1d-28b6-4678-9c82-a226d3dbfd16" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15c7eea0-4b16-4edb-9e14-116e260f7cc7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_6aa6920a-f7e7-43d0-a891-ec03744636fd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15c7eea0-4b16-4edb-9e14-116e260f7cc7" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_6aa6920a-f7e7-43d0-a891-ec03744636fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_6aa6920a-f7e7-43d0-a891-ec03744636fd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_6aa6920a-f7e7-43d0-a891-ec03744636fd" xlink:to="loc_us-gaap_EquityComponentDomain_6aa6920a-f7e7-43d0-a891-ec03744636fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_61d92530-87a9-44a5-86b4-585c778cce1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_6aa6920a-f7e7-43d0-a891-ec03744636fd" xlink:to="loc_us-gaap_EquityComponentDomain_61d92530-87a9-44a5-86b4-585c778cce1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_50bf49e1-e507-42d4-aeb8-92ef6ffaaace" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_61d92530-87a9-44a5-86b4-585c778cce1a" xlink:to="loc_us-gaap_CommonStockMember_50bf49e1-e507-42d4-aeb8-92ef6ffaaace" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_87ce1151-0df4-4c37-a4b9-2ff02d4a6dac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15c7eea0-4b16-4edb-9e14-116e260f7cc7" xlink:to="loc_us-gaap_AwardTypeAxis_87ce1151-0df4-4c37-a4b9-2ff02d4a6dac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_87ce1151-0df4-4c37-a4b9-2ff02d4a6dac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_87ce1151-0df4-4c37-a4b9-2ff02d4a6dac" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_87ce1151-0df4-4c37-a4b9-2ff02d4a6dac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0d8caa53-6645-484f-8f9a-90e27dcc4095" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_87ce1151-0df4-4c37-a4b9-2ff02d4a6dac" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0d8caa53-6645-484f-8f9a-90e27dcc4095" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_0b1050d8-03ff-469d-a255-7da217b8e4c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0d8caa53-6645-484f-8f9a-90e27dcc4095" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_0b1050d8-03ff-469d-a255-7da217b8e4c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_4630c011-6ff9-4d4e-a425-7746481d2c54" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_14227d1d-28b6-4678-9c82-a226d3dbfd16" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_4630c011-6ff9-4d4e-a425-7746481d2c54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_3f123d1f-fc45-4b1e-a12f-cc6a8e7b33e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_14227d1d-28b6-4678-9c82-a226d3dbfd16" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_3f123d1f-fc45-4b1e-a12f-cc6a8e7b33e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RestrictedStockUnitDividendEquivalents_c3c21dd9-c45f-4759-b88b-5b51fc5e857b" xlink:href="jrvr-20250331.xsd#jrvr_RestrictedStockUnitDividendEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_14227d1d-28b6-4678-9c82-a226d3dbfd16" xlink:to="loc_jrvr_RestrictedStockUnitDividendEquivalents_c3c21dd9-c45f-4759-b88b-5b51fc5e857b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_d49a3010-de52-4329-9ab3-2dbb268b60a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_14227d1d-28b6-4678-9c82-a226d3dbfd16" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_d49a3010-de52-4329-9ab3-2dbb268b60a8" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsEquityIncentivePlansDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#CapitalStockandEquityAwardsEquityIncentivePlansDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/CapitalStockandEquityAwardsEquityIncentivePlansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_10e55da0-40c3-4f4b-90b8-be2f0737accb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_10e55da0-40c3-4f4b-90b8-be2f0737accb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_50a9d660-28a6-4c55-a7d5-3235632458a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_10e55da0-40c3-4f4b-90b8-be2f0737accb" xlink:to="loc_us-gaap_PlanNameAxis_50a9d660-28a6-4c55-a7d5-3235632458a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_50a9d660-28a6-4c55-a7d5-3235632458a2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_50a9d660-28a6-4c55-a7d5-3235632458a2" xlink:to="loc_us-gaap_PlanNameDomain_50a9d660-28a6-4c55-a7d5-3235632458a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_d8f682c0-6fa7-455f-b577-a7c346b4cbe1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_50a9d660-28a6-4c55-a7d5-3235632458a2" xlink:to="loc_us-gaap_PlanNameDomain_d8f682c0-6fa7-455f-b577-a7c346b4cbe1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LongTermIncentivePlan2014Member_afbe3c06-b1e6-4eb7-994b-f838d072d93c" xlink:href="jrvr-20250331.xsd#jrvr_LongTermIncentivePlan2014Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_d8f682c0-6fa7-455f-b577-a7c346b4cbe1" xlink:to="loc_jrvr_LongTermIncentivePlan2014Member_afbe3c06-b1e6-4eb7-994b-f838d072d93c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NonEmployeeDirectorIncentivePlan2014Member_3491e122-e461-4e79-984e-e3b704d4efd8" xlink:href="jrvr-20250331.xsd#jrvr_NonEmployeeDirectorIncentivePlan2014Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_d8f682c0-6fa7-455f-b577-a7c346b4cbe1" xlink:to="loc_jrvr_NonEmployeeDirectorIncentivePlan2014Member_3491e122-e461-4e79-984e-e3b704d4efd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_8442e2e4-c859-4359-b849-a1169cb321b7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_10e55da0-40c3-4f4b-90b8-be2f0737accb" xlink:to="loc_us-gaap_AwardTypeAxis_8442e2e4-c859-4359-b849-a1169cb321b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8442e2e4-c859-4359-b849-a1169cb321b7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_8442e2e4-c859-4359-b849-a1169cb321b7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8442e2e4-c859-4359-b849-a1169cb321b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9a5873f0-6407-4161-9b9a-c2357f040642" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_8442e2e4-c859-4359-b849-a1169cb321b7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9a5873f0-6407-4161-9b9a-c2357f040642" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PRSUMember_129609a0-0d31-47c0-aaef-f8d41921f7f3" xlink:href="jrvr-20250331.xsd#jrvr_PRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9a5873f0-6407-4161-9b9a-c2357f040642" xlink:to="loc_jrvr_PRSUMember_129609a0-0d31-47c0-aaef-f8d41921f7f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_0975d9d5-dccf-45ae-b54b-9ea722ed128a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_0975d9d5-dccf-45ae-b54b-9ea722ed128a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_a213e768-2fd6-4aca-992d-57fb4198c2f9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_a213e768-2fd6-4aca-992d-57fb4198c2f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardContingentRightNumberOfSharesToBeReceived_9aa0941f-cea0-4ac8-ab99-fcb7e7532f5f" xlink:href="jrvr-20250331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardContingentRightNumberOfSharesToBeReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardContingentRightNumberOfSharesToBeReceived_9aa0941f-cea0-4ac8-ab99-fcb7e7532f5f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementThreshold_39b12bdf-82d8-4809-afce-140c70a461e7" xlink:href="jrvr-20250331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementThreshold_39b12bdf-82d8-4809-afce-140c70a461e7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_cda684b7-48d6-4c1c-9d98-bbe8b3723bc6" xlink:href="jrvr-20250331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_cda684b7-48d6-4c1c-9d98-bbe8b3723bc6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementMaximum_8b9cc2b4-c125-4d47-969a-27c3a7ceadaa" xlink:href="jrvr-20250331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8f53d927-3097-44aa-bf3f-7af9ef7cf9c2" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementMaximum_8b9cc2b4-c125-4d47-969a-27c3a7ceadaa" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsScheduleofRSUActivityDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#CapitalStockandEquityAwardsScheduleofRSUActivityDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/CapitalStockandEquityAwardsScheduleofRSUActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e78d41e9-d799-4d22-b6cf-057275d08d17" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_89d20a66-0ae8-4e92-9d09-40f3b072b222" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e78d41e9-d799-4d22-b6cf-057275d08d17" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_89d20a66-0ae8-4e92-9d09-40f3b072b222" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_496698eb-8f23-433f-9e3d-7787f3937154" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_89d20a66-0ae8-4e92-9d09-40f3b072b222" xlink:to="loc_us-gaap_AwardTypeAxis_496698eb-8f23-433f-9e3d-7787f3937154" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_496698eb-8f23-433f-9e3d-7787f3937154_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_496698eb-8f23-433f-9e3d-7787f3937154" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_496698eb-8f23-433f-9e3d-7787f3937154_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1581d7ae-6993-4421-93a2-87c4a5441a60" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_496698eb-8f23-433f-9e3d-7787f3937154" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1581d7ae-6993-4421-93a2-87c4a5441a60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_092d420b-dee6-44c8-a68f-8336e5dc3821" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1581d7ae-6993-4421-93a2-87c4a5441a60" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_092d420b-dee6-44c8-a68f-8336e5dc3821" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PRSUMember_f0fa1bcb-8e05-4cf0-a004-0adc5febc329" xlink:href="jrvr-20250331.xsd#jrvr_PRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1581d7ae-6993-4421-93a2-87c4a5441a60" xlink:to="loc_jrvr_PRSUMember_f0fa1bcb-8e05-4cf0-a004-0adc5febc329" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_f66a0220-cb83-4ae4-b4ef-6ab0a8adb025" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_89d20a66-0ae8-4e92-9d09-40f3b072b222" xlink:to="loc_srt_TitleOfIndividualAxis_f66a0220-cb83-4ae4-b4ef-6ab0a8adb025" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_f66a0220-cb83-4ae4-b4ef-6ab0a8adb025_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_f66a0220-cb83-4ae4-b4ef-6ab0a8adb025" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_f66a0220-cb83-4ae4-b4ef-6ab0a8adb025_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_0103f542-e372-4296-a9e6-0024395eaf97" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_f66a0220-cb83-4ae4-b4ef-6ab0a8adb025" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_0103f542-e372-4296-a9e6-0024395eaf97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NonemployeeDirectorsMember_c5ecf219-cf02-4c86-8d40-3f97ba91edc8" xlink:href="jrvr-20250331.xsd#jrvr_NonemployeeDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_0103f542-e372-4296-a9e6-0024395eaf97" xlink:to="loc_jrvr_NonemployeeDirectorsMember_c5ecf219-cf02-4c86-8d40-3f97ba91edc8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f44c5f39-a6d8-4dfd-a634-40f441c03813" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e78d41e9-d799-4d22-b6cf-057275d08d17" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f44c5f39-a6d8-4dfd-a634-40f441c03813" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_b23995ae-e0d8-4a7e-93cd-5062bccc2287" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f44c5f39-a6d8-4dfd-a634-40f441c03813" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_b23995ae-e0d8-4a7e-93cd-5062bccc2287" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_ec4f238d-6593-4719-8bfe-56fe90c9a5cf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f44c5f39-a6d8-4dfd-a634-40f441c03813" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_ec4f238d-6593-4719-8bfe-56fe90c9a5cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_a877ffb4-c897-4f0e-b126-ae01e3d4f533" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f44c5f39-a6d8-4dfd-a634-40f441c03813" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_a877ffb4-c897-4f0e-b126-ae01e3d4f533" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_a23bc870-8922-4df2-b067-ca4b6bc4b122" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_f44c5f39-a6d8-4dfd-a634-40f441c03813" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_a23bc870-8922-4df2-b067-ca4b6bc4b122" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_bed6c671-9779-49e8-beac-5b7e6316d686" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_a20e80aa-ff9b-49e6-83ab-0bae188dd58e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e78d41e9-d799-4d22-b6cf-057275d08d17" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_a20e80aa-ff9b-49e6-83ab-0bae188dd58e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_2dea5fba-bf9e-47b3-9b19-e451e467ea90" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_a20e80aa-ff9b-49e6-83ab-0bae188dd58e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_2dea5fba-bf9e-47b3-9b19-e451e467ea90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_1e4484f6-2178-4e37-aeb4-84f3df41bd6f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_a20e80aa-ff9b-49e6-83ab-0bae188dd58e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_1e4484f6-2178-4e37-aeb4-84f3df41bd6f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_0af5530d-7ca0-41fc-a64b-b6d5ddbb3f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_a20e80aa-ff9b-49e6-83ab-0bae188dd58e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_0af5530d-7ca0-41fc-a64b-b6d5ddbb3f9d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_d2e02098-3378-4e00-af4c-0be68122f4b0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_a20e80aa-ff9b-49e6-83ab-0bae188dd58e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_d2e02098-3378-4e00-af4c-0be68122f4b0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_b536b07c-2878-4f80-a31b-590778e00445" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_1ad3eda5-5ad2-41b5-a19a-7aea18c179c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e78d41e9-d799-4d22-b6cf-057275d08d17" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_1ad3eda5-5ad2-41b5-a19a-7aea18c179c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_ffd09b90-f955-4746-95bb-243a03845694" xlink:href="jrvr-20250331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e78d41e9-d799-4d22-b6cf-057275d08d17" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_ffd09b90-f955-4746-95bb-243a03845694" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsOptionDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#CapitalStockandEquityAwardsOptionDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/CapitalStockandEquityAwardsOptionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7768da6c-77b9-4ec3-aaa6-11c1b36262b3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_29b8767f-cacc-4acf-aaea-fa9617f9868a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7768da6c-77b9-4ec3-aaa6-11c1b36262b3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_29b8767f-cacc-4acf-aaea-fa9617f9868a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_765bebc9-545d-4352-8609-46fe81516d33" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_29b8767f-cacc-4acf-aaea-fa9617f9868a" xlink:to="loc_us-gaap_AwardTypeAxis_765bebc9-545d-4352-8609-46fe81516d33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_765bebc9-545d-4352-8609-46fe81516d33_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_765bebc9-545d-4352-8609-46fe81516d33" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_765bebc9-545d-4352-8609-46fe81516d33_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6021429e-ed48-442a-83ab-8f65e909d9fe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_765bebc9-545d-4352-8609-46fe81516d33" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6021429e-ed48-442a-83ab-8f65e909d9fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_e833d695-5274-4ffc-b624-1c6aeb6d4e57" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6021429e-ed48-442a-83ab-8f65e909d9fe" xlink:to="loc_us-gaap_EmployeeStockOptionMember_e833d695-5274-4ffc-b624-1c6aeb6d4e57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_982479c1-642e-41ab-9a56-32f97c61cdc1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7768da6c-77b9-4ec3-aaa6-11c1b36262b3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_982479c1-642e-41ab-9a56-32f97c61cdc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_85f0329f-8ff7-4096-b655-50e8bf9894fb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7768da6c-77b9-4ec3-aaa6-11c1b36262b3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_85f0329f-8ff7-4096-b655-50e8bf9894fb" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsCompensationExpenseDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#CapitalStockandEquityAwardsCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/CapitalStockandEquityAwardsCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78655c4e-8ac3-4888-b7e3-0d606d24a449" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_822cdcb2-1f5e-477e-a2c0-318cd03e12b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78655c4e-8ac3-4888-b7e3-0d606d24a449" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_822cdcb2-1f5e-477e-a2c0-318cd03e12b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_4110fdd1-be14-437a-924a-99e18631d2af" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_822cdcb2-1f5e-477e-a2c0-318cd03e12b5" xlink:to="loc_us-gaap_AwardTypeAxis_4110fdd1-be14-437a-924a-99e18631d2af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4110fdd1-be14-437a-924a-99e18631d2af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_4110fdd1-be14-437a-924a-99e18631d2af" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4110fdd1-be14-437a-924a-99e18631d2af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_92689340-61ef-406c-a9d4-185286b2ccca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_4110fdd1-be14-437a-924a-99e18631d2af" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_92689340-61ef-406c-a9d4-185286b2ccca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_c2ac2098-9529-4998-9537-ad7c2fffac84" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_92689340-61ef-406c-a9d4-185286b2ccca" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_c2ac2098-9529-4998-9537-ad7c2fffac84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_1d5b092a-d6fe-46d7-a1ce-7545df6ffe4c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78655c4e-8ac3-4888-b7e3-0d606d24a449" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_1d5b092a-d6fe-46d7-a1ce-7545df6ffe4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_666bf7a0-39ef-456e-abe3-9dd24ddb020f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78655c4e-8ac3-4888-b7e3-0d606d24a449" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_666bf7a0-39ef-456e-abe3-9dd24ddb020f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="jrvr-20250331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_24cfff51-af0f-41da-8bd0-964e04e69d90" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_24cfff51-af0f-41da-8bd0-964e04e69d90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_24cfff51-af0f-41da-8bd0-964e04e69d90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_24cfff51-af0f-41da-8bd0-964e04e69d90" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_24cfff51-af0f-41da-8bd0-964e04e69d90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_ac438630-c32f-490d-b20e-3c6d0e7889cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_24cfff51-af0f-41da-8bd0-964e04e69d90" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_ac438630-c32f-490d-b20e-3c6d0e7889cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_8e03d0d2-8dce-4f27-88e0-e76768e0a9ba" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_ac438630-c32f-490d-b20e-3c6d0e7889cd" xlink:to="loc_us-gaap_SubsequentEventMember_8e03d0d2-8dce-4f27-88e0-e76768e0a9ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_aaad95b7-926c-48e8-b16d-3c1f6bd2cec5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:to="loc_us-gaap_StatementClassOfStockAxis_aaad95b7-926c-48e8-b16d-3c1f6bd2cec5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_aaad95b7-926c-48e8-b16d-3c1f6bd2cec5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_aaad95b7-926c-48e8-b16d-3c1f6bd2cec5" xlink:to="loc_us-gaap_ClassOfStockDomain_aaad95b7-926c-48e8-b16d-3c1f6bd2cec5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_4309255d-61ed-4181-8a4f-1fc98ee204f0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_aaad95b7-926c-48e8-b16d-3c1f6bd2cec5" xlink:to="loc_us-gaap_ClassOfStockDomain_4309255d-61ed-4181-8a4f-1fc98ee204f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_dafefc50-bec1-4bcb-b9ea-20b430d3cdf0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_4309255d-61ed-4181-8a4f-1fc98ee204f0" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_dafefc50-bec1-4bcb-b9ea-20b430d3cdf0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAxis_ef687cfb-edda-4d19-be88-8160e72116fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:to="loc_us-gaap_DividendsAxis_ef687cfb-edda-4d19-be88-8160e72116fc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_ef687cfb-edda-4d19-be88-8160e72116fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DividendsAxis_ef687cfb-edda-4d19-be88-8160e72116fc" xlink:to="loc_us-gaap_DividendsDomain_ef687cfb-edda-4d19-be88-8160e72116fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_f41083e8-3ba8-40d7-9a0f-47639c9480b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DividendsAxis_ef687cfb-edda-4d19-be88-8160e72116fc" xlink:to="loc_us-gaap_DividendsDomain_f41083e8-3ba8-40d7-9a0f-47639c9480b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_O2025Q1DividendsMember_91efccfd-923b-4045-a49b-5aa4f5bc9024" xlink:href="jrvr-20250331.xsd#jrvr_O2025Q1DividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_f41083e8-3ba8-40d7-9a0f-47639c9480b9" xlink:to="loc_jrvr_O2025Q1DividendsMember_91efccfd-923b-4045-a49b-5aa4f5bc9024" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_7d24de8b-068c-4e43-ab81-9bf1d9fb7d5f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_7d24de8b-068c-4e43-ab81-9bf1d9fb7d5f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_7d24de8b-068c-4e43-ab81-9bf1d9fb7d5f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7d24de8b-068c-4e43-ab81-9bf1d9fb7d5f" xlink:to="loc_us-gaap_SegmentDomain_7d24de8b-068c-4e43-ab81-9bf1d9fb7d5f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_0660d815-e38e-455e-8d0f-629de24b8f62" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7d24de8b-068c-4e43-ab81-9bf1d9fb7d5f" xlink:to="loc_us-gaap_SegmentDomain_0660d815-e38e-455e-8d0f-629de24b8f62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_642c094b-69b2-41fa-b7d6-560c69f3cb2d" xlink:href="jrvr-20250331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_0660d815-e38e-455e-8d0f-629de24b8f62" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_642c094b-69b2-41fa-b7d6-560c69f3cb2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_c2f2c258-2f83-44f0-99b5-db12945cf318" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_c2f2c258-2f83-44f0-99b5-db12945cf318" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_c2f2c258-2f83-44f0-99b5-db12945cf318_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_c2f2c258-2f83-44f0-99b5-db12945cf318" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_c2f2c258-2f83-44f0-99b5-db12945cf318_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_6e2da4a1-9b64-4c7a-a946-fe2d8702a17d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_c2f2c258-2f83-44f0-99b5-db12945cf318" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_6e2da4a1-9b64-4c7a-a946-fe2d8702a17d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_df6691ab-9b94-4ece-aee1-39ebe1c41114" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_6e2da4a1-9b64-4c7a-a946-fe2d8702a17d" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_df6691ab-9b94-4ece-aee1-39ebe1c41114" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8c0e0c06-8226-4328-92dc-bf333583b665" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_15427a90-c230-40a2-8249-50dc711b8f27" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8c0e0c06-8226-4328-92dc-bf333583b665" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_8c0e0c06-8226-4328-92dc-bf333583b665_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8c0e0c06-8226-4328-92dc-bf333583b665" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_8c0e0c06-8226-4328-92dc-bf333583b665_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_41515067-2311-4af5-ac61-bd91ee5bb7d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8c0e0c06-8226-4328-92dc-bf333583b665" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_41515067-2311-4af5-ac61-bd91ee5bb7d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_JrgReMember_0e573b23-8293-4001-9364-cdd1a4977f20" xlink:href="jrvr-20250331.xsd#jrvr_JrgReMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_41515067-2311-4af5-ac61-bd91ee5bb7d4" xlink:to="loc_jrvr_JrgReMember_0e573b23-8293-4001-9364-cdd1a4977f20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommitmentToInvestmentInNotes_6c97461e-43eb-4de7-b6ff-233211298f4e" xlink:href="jrvr-20250331.xsd#jrvr_CommitmentToInvestmentInNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_jrvr_CommitmentToInvestmentInNotes_6c97461e-43eb-4de7-b6ff-233211298f4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationAmountsOfMaterialContingentLiabilitiesRemaining_d840f182-4d88-428b-81fc-a18989cbb986" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationAmountsOfMaterialContingentLiabilitiesRemaining"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationAmountsOfMaterialContingentLiabilitiesRemaining_d840f182-4d88-428b-81fc-a18989cbb986" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment_ea19eb67-0d82-4af1-ac94-821681bb93ce" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment_ea19eb67-0d82-4af1-ac94-821681bb93ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationDownwardAdjustmentPaid_183e209c-a9a6-4621-a168-44ea5200849d" xlink:href="jrvr-20250331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationDownwardAdjustmentPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationDownwardAdjustmentPaid_183e209c-a9a6-4621-a168-44ea5200849d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_a1928946-8ea2-41eb-9972-389b9487c03e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_a1928946-8ea2-41eb-9972-389b9487c03e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_a7549b23-3fe7-436f-ab23-004b8d1a6b6a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendPayableDateToBePaidDayMonthAndYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_a7549b23-3fe7-436f-ab23-004b8d1a6b6a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_76fdbc28-71db-4213-9a1c-cbf1d5f006ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsPayableDateOfRecordDayMonthAndYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_76fdbc28-71db-4213-9a1c-cbf1d5f006ec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_aca4169a-5ab3-4b52-980d-a1eaa6aefa0d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_209d3296-313d-45fd-92a5-8fa3c6fac21a" xlink:to="loc_us-gaap_DividendsPreferredStock_aca4169a-5ab3-4b52-980d-a1eaa6aefa0d" xlink:type="arc" order="7"/>
  </link:definitionLink>
</link:linkbase>
