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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ce7a5-456e-7556-921b-96e45497b599,g:b29dc00c-3c67-48e5-8a7a-dfda811b68ad-->
<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-20260331.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_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ce7a5-4766-70f6-b320-96c38290cc3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_StatementTable_019ce7a5-4766-70f6-b320-96c38290cc3c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4766-7432-a982-25b4312dcbf2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ce7a5-4766-70f6-b320-96c38290cc3c" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4766-7432-a982-25b4312dcbf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4766-7432-a982-25b4312dcbf2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4766-7432-a982-25b4312dcbf2" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4766-7432-a982-25b4312dcbf2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4766-7bb7-b3c0-c4109990b037" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4766-7432-a982-25b4312dcbf2" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4766-7bb7-b3c0-c4109990b037" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4766-759c-8957-8160956561f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4766-7bb7-b3c0-c4109990b037" xlink:to="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4766-759c-8957-8160956561f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019ce7a5-4766-7a94-aecd-a6d3c94676a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019ce7a5-4766-7a94-aecd-a6d3c94676a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCost_019ce7a5-4766-7c9f-8a92-d03d048710db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCost_019ce7a5-4766-7c9f-8a92-d03d048710db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_019ce7a5-4766-73ba-b3a1-919f81fcaf56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_019ce7a5-4766-73ba-b3a1-919f81fcaf56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_019ce7a5-4766-79b0-a0d9-9f3e4b6dee87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_019ce7a5-4766-79b0-a0d9-9f3e4b6dee87" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019ce7a5-4766-7fa6-9a14-884242051ace" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019ce7a5-4766-7fa6-9a14-884242051ace" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ce7a5-4766-77a4-87ef-2610f0f4a39d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ce7a5-4766-77a4-87ef-2610f0f4a39d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019ce7a5-4766-7bb9-aa11-0106c0c85f4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019ce7a5-4766-7bb9-aa11-0106c0c85f4e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019ce7a5-4766-777d-92db-34c8e67daaf3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_CommonStockSharesIssued_019ce7a5-4766-777d-92db-34c8e67daaf3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ce7a5-4766-7ed9-aff1-128ddb183a67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ce7a5-4766-7ed9-aff1-128ddb183a67" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ce7a5-4766-7cce-b8b3-853295acfdf0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ce7a5-4766-7cce-b8b3-853295acfdf0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019ce7a5-4766-7285-99e3-e3bdd063662a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019ce7a5-4766-7285-99e3-e3bdd063662a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019ce7a5-4766-7447-a8f9-507f921b122c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019ce7a5-4766-7447-a8f9-507f921b122c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ce7a5-4766-74f2-ad38-622438431e4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-7656-b9c2-fb4f7f0451d9" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019ce7a5-4766-74f2-ad38-622438431e4a" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CondensedConsolidatedStatementsofChangesinShareholdersEquityUnaudited" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4766-792a-a1b1-7cee57940836" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ce7a5-4766-7c0a-909d-566803264948" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-792a-a1b1-7cee57940836" xlink:to="loc_us-gaap_StatementTable_019ce7a5-4766-7c0a-909d-566803264948" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4766-7399-9762-5670b8e551cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ce7a5-4766-7c0a-909d-566803264948" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4766-7399-9762-5670b8e551cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7399-9762-5670b8e551cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4766-7399-9762-5670b8e551cf" xlink:to="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7399-9762-5670b8e551cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7bd5-bd7e-ca02cdedcc4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4766-7399-9762-5670b8e551cf" xlink:to="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7bd5-bd7e-ca02cdedcc4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ce7a5-4766-7af0-8458-0b4b9416f375" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7bd5-bd7e-ca02cdedcc4c" xlink:to="loc_us-gaap_CommonStockMember_019ce7a5-4766-7af0-8458-0b4b9416f375" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_019ce7a5-4766-7033-8901-8847bd7058c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7bd5-bd7e-ca02cdedcc4c" xlink:to="loc_us-gaap_PreferredStockMember_019ce7a5-4766-7033-8901-8847bd7058c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019ce7a5-4766-7be2-8a01-59255ab8f076" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7bd5-bd7e-ca02cdedcc4c" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019ce7a5-4766-7be2-8a01-59255ab8f076" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019ce7a5-4766-7867-85f2-282fe0cc1308" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7bd5-bd7e-ca02cdedcc4c" xlink:to="loc_us-gaap_RetainedEarningsMember_019ce7a5-4766-7867-85f2-282fe0cc1308" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ce7a5-4766-7690-995c-2735e676e66c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce7a5-4766-7bd5-bd7e-ca02cdedcc4c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ce7a5-4766-7690-995c-2735e676e66c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ce7a5-4766-792a-a1b1-7cee57940836" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ce7a5-4766-78e0-9a4d-f46e623db1b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ce7a5-4766-78e0-9a4d-f46e623db1b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ce7a5-4766-71b3-b72d-f1387bfb656a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_StockholdersEquity_019ce7a5-4766-71b3-b72d-f1387bfb656a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ce7a5-4766-7b7b-b2f5-cebd8c5894a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_NetIncomeLoss_019ce7a5-4766-7b7b-b2f5-cebd8c5894a1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ce7a5-4766-7082-8514-40525c2eaf63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ce7a5-4766-7082-8514-40525c2eaf63" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019ce7a5-4766-74ff-9569-f6fcf55e3738" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019ce7a5-4766-74ff-9569-f6fcf55e3738" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019ce7a5-4766-734f-8913-d443ae30a885" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019ce7a5-4766-734f-8913-d443ae30a885" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ce7a5-4766-72d0-91d0-fb6d33f8ef78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ce7a5-4766-72d0-91d0-fb6d33f8ef78" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_019ce7a5-4766-700d-a38f-013667e1ed14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_DividendsPreferredStock_019ce7a5-4766-700d-a38f-013667e1ed14" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_019ce7a5-4766-70f2-809f-744b72ed1973" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ce7a5-4766-7884-96b8-63c29a6313a8" xlink:to="loc_us-gaap_DividendsCommonStock_019ce7a5-4766-70f2-809f-744b72ed1973" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ce7a5-4766-7161-8a4c-2ea1c616266f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ce7a5-4766-7bce-93bd-147b9b2aba4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/AccountingPoliciesDetails" xlink:type="simple" xlink:href="jrvr-20260331.xsd#AccountingPoliciesDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/AccountingPoliciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AccountingPoliciesLineItems_019ce7a5-4766-747c-86dc-fc65e1119d65" xlink:href="jrvr-20260331.xsd#jrvr_AccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AccountingPoliciesTable_019ce7a5-4766-729d-a37d-a422166edd31" xlink:href="jrvr-20260331.xsd#jrvr_AccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_AccountingPoliciesLineItems_019ce7a5-4766-747c-86dc-fc65e1119d65" xlink:to="loc_jrvr_AccountingPoliciesTable_019ce7a5-4766-729d-a37d-a422166edd31" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019ce7a5-4766-75c8-9fa7-5dfd13b7adce" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_AccountingPoliciesTable_019ce7a5-4766-729d-a37d-a422166edd31" xlink:to="loc_srt_StatementGeographicalAxis_019ce7a5-4766-75c8-9fa7-5dfd13b7adce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce7a5-4766-75c8-9fa7-5dfd13b7adce_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019ce7a5-4766-75c8-9fa7-5dfd13b7adce" xlink:to="loc_srt_SegmentGeographicalDomain_019ce7a5-4766-75c8-9fa7-5dfd13b7adce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ce7a5-4766-71fc-a3e4-1a8de7f8c774" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019ce7a5-4766-75c8-9fa7-5dfd13b7adce" xlink:to="loc_srt_SegmentGeographicalDomain_019ce7a5-4766-71fc-a3e4-1a8de7f8c774" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019ce7a5-4766-7305-b4da-d0971a2c5d1f" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ce7a5-4766-71fc-a3e4-1a8de7f8c774" xlink:to="loc_country_US_019ce7a5-4766-7305-b4da-d0971a2c5d1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfInsuranceCompanies_019ce7a5-4766-7c94-a997-1d600ef6de13" xlink:href="jrvr-20260331.xsd#jrvr_NumberOfInsuranceCompanies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AccountingPoliciesLineItems_019ce7a5-4766-747c-86dc-fc65e1119d65" xlink:to="loc_jrvr_NumberOfInsuranceCompanies_019ce7a5-4766-7c94-a997-1d600ef6de13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_019ce7a5-4766-7b00-baef-d520bdf6ea04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AccountingPoliciesLineItems_019ce7a5-4766-747c-86dc-fc65e1119d65" xlink:to="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_019ce7a5-4766-7b00-baef-d520bdf6ea04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019ce7a5-4766-758a-9d83-e90def485999" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AccountingPoliciesLineItems_019ce7a5-4766-747c-86dc-fc65e1119d65" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019ce7a5-4766-758a-9d83-e90def485999" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/DiscontinuedOperationsNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-7367-af9d-a73b71eaa3a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019ce7a5-4818-78aa-9ef3-8d0d4f623a0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019ce7a5-4818-7367-af9d-a73b71eaa3a4" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019ce7a5-4818-78aa-9ef3-8d0d4f623a0b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019d42ee-4e45-7e3d-ab7a-16003172a32c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019ce7a5-4818-78aa-9ef3-8d0d4f623a0b" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019d42ee-4e45-7e3d-ab7a-16003172a32c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019d42ee-4e45-7e3d-ab7a-16003172a32c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019d42ee-4e45-7e3d-ab7a-16003172a32c" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019d42ee-4e45-7e3d-ab7a-16003172a32c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019d42ee-4e45-767a-ac30-bcaf08ffa53e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019d42ee-4e45-7e3d-ab7a-16003172a32c" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019d42ee-4e45-767a-ac30-bcaf08ffa53e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019d42ee-4e45-73ac-96f5-45c259b1ca51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019d42ee-4e45-767a-ac30-bcaf08ffa53e" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019d42ee-4e45-73ac-96f5-45c259b1ca51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019d42ee-4e45-7b6f-98f9-a2bed92ffd21" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019ce7a5-4818-78aa-9ef3-8d0d4f623a0b" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019d42ee-4e45-7b6f-98f9-a2bed92ffd21" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019d42ee-4e45-7b6f-98f9-a2bed92ffd21_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019d42ee-4e45-7b6f-98f9-a2bed92ffd21" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019d42ee-4e45-7b6f-98f9-a2bed92ffd21_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019d42ee-4e45-7195-9ddd-8b8131e2f073" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019d42ee-4e45-7b6f-98f9-a2bed92ffd21" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019d42ee-4e45-7195-9ddd-8b8131e2f073" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_JrgReMember_019d42ee-4e45-7300-aed4-f4ab8de0fc3a" xlink:href="jrvr-20260331.xsd#jrvr_JrgReMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019d42ee-4e45-7195-9ddd-8b8131e2f073" xlink:to="loc_jrvr_JrgReMember_019d42ee-4e45-7300-aed4-f4ab8de0fc3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_019d42ee-4e45-7beb-9016-301e5e480078" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019ce7a5-4818-7367-af9d-a73b71eaa3a4" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_019d42ee-4e45-7beb-9016-301e5e480078" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment_019d42ee-4e45-7e2e-9c26-9b3f5cee707b" xlink:href="jrvr-20260331.xsd#jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019ce7a5-4818-7367-af9d-a73b71eaa3a4" xlink:to="loc_jrvr_DisposalGroupIncludingDiscontinuedOperationConsiderationDownwardAdjustment_019d42ee-4e45-7e2e-9c26-9b3f5cee707b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DiscontinuedOperationsTransactionCosts_019d42ee-4e45-77f4-b5e6-9498ed1ec2a1" xlink:href="jrvr-20260331.xsd#jrvr_DiscontinuedOperationsTransactionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019ce7a5-4818-7367-af9d-a73b71eaa3a4" xlink:to="loc_jrvr_DiscontinuedOperationsTransactionCosts_019d42ee-4e45-77f4-b5e6-9498ed1ec2a1" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsScheduleofAvailableforSaleInvestmentsDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-7f44-bd79-c4fa39f516a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce7a5-4818-7ac2-a4f1-e0e7831cc613" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-7f44-bd79-c4fa39f516a8" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce7a5-4818-7ac2-a4f1-e0e7831cc613" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-72a6-b97a-59016a9f0fb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce7a5-4818-7ac2-a4f1-e0e7831cc613" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-72a6-b97a-59016a9f0fb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-72a6-b97a-59016a9f0fb3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-72a6-b97a-59016a9f0fb3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-72a6-b97a-59016a9f0fb3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-7ac6-a524-f31c8f0ce84d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-72a6-b97a-59016a9f0fb3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-7ac6-a524-f31c8f0ce84d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7193-a3d6-5ee297b5ae38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-7ac6-a524-f31c8f0ce84d" xlink:to="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7193-a3d6-5ee297b5ae38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019ce7a5-4818-7a70-8221-42845e7424d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7193-a3d6-5ee297b5ae38" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019ce7a5-4818-7a70-8221-42845e7424d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019ce7a5-4818-7add-8127-7894b12ed2cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7193-a3d6-5ee297b5ae38" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019ce7a5-4818-7add-8127-7894b12ed2cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019ce7a5-4818-714a-a24b-f96a1a757d30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7193-a3d6-5ee297b5ae38" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019ce7a5-4818-714a-a24b-f96a1a757d30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_019ce7a5-4818-74b3-8a7e-8111ba91d824" xlink:href="jrvr-20260331.xsd#jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7193-a3d6-5ee297b5ae38" xlink:to="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_019ce7a5-4818-74b3-8a7e-8111ba91d824" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019ce7a5-4818-7371-91ed-d999f3ef7382" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7193-a3d6-5ee297b5ae38" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019ce7a5-4818-7371-91ed-d999f3ef7382" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019ce7a5-4818-7390-9230-ce73b92f1f26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-7f44-bd79-c4fa39f516a8" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019ce7a5-4818-7390-9230-ce73b92f1f26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019ce7a5-4818-78f8-9c71-4234018a3dc0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-7f44-bd79-c4fa39f516a8" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019ce7a5-4818-78f8-9c71-4234018a3dc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019ce7a5-4818-726c-a65f-4f027cac5228" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-7f44-bd79-c4fa39f516a8" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019ce7a5-4818-726c-a65f-4f027cac5228" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce7a5-4818-7979-8586-c67b4bdfa3b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-7f44-bd79-c4fa39f516a8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce7a5-4818-7979-8586-c67b4bdfa3b0" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsScheduleofGrossUnrealizedLossesandFairValueDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce7a5-4818-7196-a4b2-4fc630854935" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce7a5-4818-7196-a4b2-4fc630854935" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-7366-b448-1287a2ef465f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019ce7a5-4818-7196-a4b2-4fc630854935" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-7366-b448-1287a2ef465f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-7366-b448-1287a2ef465f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-7366-b448-1287a2ef465f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-7366-b448-1287a2ef465f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-715d-beec-e133f2ba99c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-7366-b448-1287a2ef465f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-715d-beec-e133f2ba99c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7e73-a6f4-85774b33c473" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-715d-beec-e133f2ba99c4" xlink:to="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7e73-a6f4-85774b33c473" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019ce7a5-4818-73b0-b997-45a7ab9c7b05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7e73-a6f4-85774b33c473" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019ce7a5-4818-73b0-b997-45a7ab9c7b05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019ce7a5-4818-7fb4-8c17-558b2262b8ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7e73-a6f4-85774b33c473" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019ce7a5-4818-7fb4-8c17-558b2262b8ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019ce7a5-4818-75ae-a001-46a8801c9a4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7e73-a6f4-85774b33c473" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019ce7a5-4818-75ae-a001-46a8801c9a4f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_019ce7a5-4818-7d23-8880-102c82c30c32" xlink:href="jrvr-20260331.xsd#jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7e73-a6f4-85774b33c473" xlink:to="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_019ce7a5-4818-7d23-8880-102c82c30c32" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019ce7a5-4818-78b4-912a-6657b6a0cdde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4818-7e73-a6f4-85774b33c473" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019ce7a5-4818-78b4-912a-6657b6a0cdde" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019ce7a5-4818-7e44-be04-3bcb5ce72f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019ce7a5-4818-7e44-be04-3bcb5ce72f9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019ce7a5-4818-7d60-a3b7-10434144274e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019ce7a5-4818-7d60-a3b7-10434144274e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019ce7a5-4818-7676-82cb-25de698abe28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019ce7a5-4818-7676-82cb-25de698abe28" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019ce7a5-4818-7ca6-95de-6d8c0fe6b8bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019ce7a5-4818-7ca6-95de-6d8c0fe6b8bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019ce7a5-4818-701f-a881-7ba975e6bcac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019ce7a5-4818-701f-a881-7ba975e6bcac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019ce7a5-4818-74d5-92b2-2f45d95bb82f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019ce7a5-4818-742b-894b-60926b44f0c6" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019ce7a5-4818-74d5-92b2-2f45d95bb82f" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_019ce7a5-4818-7d10-b381-4e2adcdf562c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGainLossOnInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_019ce7a5-4818-7d10-b381-4e2adcdf562c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d42df-d277-7583-96a1-ede61fd3b0a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_019ce7a5-4818-7d10-b381-4e2adcdf562c" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d42df-d277-7583-96a1-ede61fd3b0a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d42df-d277-7583-96a1-ede61fd3b0a4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d42df-d277-7583-96a1-ede61fd3b0a4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d42df-d277-7583-96a1-ede61fd3b0a4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d42df-d277-7ecf-b95d-403baa2c7fc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d42df-d277-7583-96a1-ede61fd3b0a4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d42df-d277-7ecf-b95d-403baa2c7fc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019d42df-d277-7f52-a1fd-2d784ace61e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d42df-d277-7ecf-b95d-403baa2c7fc2" xlink:to="loc_us-gaap_DebtSecuritiesMember_019d42df-d277-7f52-a1fd-2d784ace61e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingStandardPoorsAxis_019d42df-d277-7387-a689-3b4802d38203" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CreditRatingStandardPoorsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_019ce7a5-4818-7d10-b381-4e2adcdf562c" xlink:to="loc_srt_CreditRatingStandardPoorsAxis_019d42df-d277-7387-a689-3b4802d38203" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ExternalCreditRatingStandardPoorsMember_019d42df-d277-7387-a689-3b4802d38203_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ExternalCreditRatingStandardPoorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CreditRatingStandardPoorsAxis_019d42df-d277-7387-a689-3b4802d38203" xlink:to="loc_srt_ExternalCreditRatingStandardPoorsMember_019d42df-d277-7387-a689-3b4802d38203_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ExternalCreditRatingStandardPoorsMember_019d42df-d277-7246-9c94-f8420eff8c5d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ExternalCreditRatingStandardPoorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CreditRatingStandardPoorsAxis_019d42df-d277-7387-a689-3b4802d38203" xlink:to="loc_srt_ExternalCreditRatingStandardPoorsMember_019d42df-d277-7246-9c94-f8420eff8c5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_StandardPoorsBBBorBetterRatingMember_019d42df-d277-7109-9704-3a8818325557" xlink:href="jrvr-20260331.xsd#jrvr_StandardPoorsBBBorBetterRatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ExternalCreditRatingStandardPoorsMember_019d42df-d277-7246-9c94-f8420eff8c5d" xlink:to="loc_jrvr_StandardPoorsBBBorBetterRatingMember_019d42df-d277-7109-9704-3a8818325557" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019d42e0-212f-769a-ad53-655d409f0966" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsTable_019ce7a5-4818-7d10-b381-4e2adcdf562c" xlink:to="loc_us-gaap_InvestmentTypeAxis_019d42e0-212f-769a-ad53-655d409f0966" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019d42e0-212f-769a-ad53-655d409f0966_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019d42e0-212f-769a-ad53-655d409f0966" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019d42e0-212f-769a-ad53-655d409f0966_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019d42e0-212f-71d7-9670-3f61f7b3d8b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019d42e0-212f-769a-ad53-655d409f0966" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019d42e0-212f-71d7-9670-3f61f7b3d8b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanParticipationsAndAssignmentsMember_019ddab4-37cd-7491-af11-1fb4ccc7b93d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoanParticipationsAndAssignmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d42e0-212f-71d7-9670-3f61f7b3d8b5" xlink:to="loc_us-gaap_LoanParticipationsAndAssignmentsMember_019ddab4-37cd-7491-af11-1fb4ccc7b93d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SixthStreetMember_019ddabb-2a9c-7876-995a-dc7fe726caea" xlink:href="jrvr-20260331.xsd#jrvr_SixthStreetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019d42e0-212f-71d7-9670-3f61f7b3d8b5" xlink:to="loc_jrvr_SixthStreetMember_019ddabb-2a9c-7876-995a-dc7fe726caea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019d42df-d277-7d37-8ca1-be004a49c3ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019d42df-d277-7d37-8ca1-be004a49c3ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019d42df-d277-719a-a623-53dc96e14bd7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019d42df-d277-719a-a623-53dc96e14bd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019d42df-d277-71f9-91c5-3e8eccc3186c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019d42df-d277-71f9-91c5-3e8eccc3186c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PercentageOfAvailableForSaleDebtSecurities_019d42df-d277-7a6d-aabd-398b97814cc1" xlink:href="jrvr-20260331.xsd#jrvr_PercentageOfAvailableForSaleDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_jrvr_PercentageOfAvailableForSaleDebtSecurities_019d42df-d277-7a6d-aabd-398b97814cc1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_019d42df-f7d5-777e-85f6-974471e5b4e8" xlink:href="jrvr-20260331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_019d42df-f7d5-777e-85f6-974471e5b4e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance_019d42df-f7d5-7e04-b212-8a33efe4a08b" xlink:href="jrvr-20260331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance_019d42df-f7d5-7e04-b212-8a33efe4a08b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_019d42df-f7d5-71af-abda-caf80fb98594" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_019d42df-f7d5-71af-abda-caf80fb98594" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_BankLoanParticipationsNetGainLoss_019d42df-f7d5-74ff-9e6b-86d920739d66" xlink:href="jrvr-20260331.xsd#jrvr_BankLoanParticipationsNetGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_jrvr_BankLoanParticipationsNetGainLoss_019d42df-f7d5-74ff-9e6b-86d920739d66" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_BankLoanParticipationsRealizedAndUnrealizedLossesCreditRelatedImpairments_019d42df-f7d5-7589-af4c-cab844b5c0cf" xlink:href="jrvr-20260331.xsd#jrvr_BankLoanParticipationsRealizedAndUnrealizedLossesCreditRelatedImpairments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_jrvr_BankLoanParticipationsRealizedAndUnrealizedLossesCreditRelatedImpairments_019d42df-f7d5-7589-af4c-cab844b5c0cf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Investments_019d42e0-212f-7e31-8fc6-4d25c80e9a2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Investments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_us-gaap_Investments_019d42e0-212f-7e31-8fc6-4d25c80e9a2a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_InvestmentCollateralizedNotesReceivable_019d42e0-212f-7059-9faf-b6b1de51c409" xlink:href="jrvr-20260331.xsd#jrvr_InvestmentCollateralizedNotesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_jrvr_InvestmentCollateralizedNotesReceivable_019d42e0-212f-7059-9faf-b6b1de51c409" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeNet_019d42e0-212f-7667-96f9-444ca84c6deb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentIncomeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_us-gaap_InvestmentIncomeNet_019d42e0-212f-7667-96f9-444ca84c6deb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommitmentToInvestInNotesReceivable_019d42e0-212f-74ad-adad-32a250e117f5" xlink:href="jrvr-20260331.xsd#jrvr_CommitmentToInvestInNotesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems_019ce7a5-4818-7ca9-8d46-94404e3dfb18" xlink:to="loc_jrvr_CommitmentToInvestInNotesReceivable_019d42e0-212f-74ad-adad-32a250e117f5" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/InvestmentsScheduleofPrivateDebtandEquityDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7b46-b01a-54fe6b148d02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7b46-b01a-54fe6b148d02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7b46-b01a-54fe6b148d02_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7b46-b01a-54fe6b148d02" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7b46-b01a-54fe6b148d02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-76d8-8d68-419245ba7b26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7b46-b01a-54fe6b148d02" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-76d8-8d68-419245ba7b26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-79f6-8188-b039dcdb4ed9" xlink:href="jrvr-20260331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-76d8-8d68-419245ba7b26" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-79f6-8188-b039dcdb4ed9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019ce7a5-4818-72d6-8c22-e594c4920eca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-76d8-8d68-419245ba7b26" xlink:to="loc_us-gaap_CorporateAndOtherMember_019ce7a5-4818-72d6-8c22-e594c4920eca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019ce7a5-4818-757f-91ab-b9ed1221204c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:to="loc_us-gaap_InvestmentTypeAxis_019ce7a5-4818-757f-91ab-b9ed1221204c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-757f-91ab-b9ed1221204c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019ce7a5-4818-757f-91ab-b9ed1221204c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-757f-91ab-b9ed1221204c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-7aa9-a796-a81d2d47b9a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019ce7a5-4818-757f-91ab-b9ed1221204c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-7aa9-a796-a81d2d47b9a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RenewableEnergyLlcsMember_019ce7a5-4818-7cfc-aa78-203087bc3502" xlink:href="jrvr-20260331.xsd#jrvr_RenewableEnergyLlcsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-7aa9-a796-a81d2d47b9a9" xlink:to="loc_jrvr_RenewableEnergyLlcsMember_019ce7a5-4818-7cfc-aa78-203087bc3502" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_019ce7a5-4818-7c21-a68e-472133272780" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-7aa9-a796-a81d2d47b9a9" xlink:to="loc_srt_PartnershipInterestMember_019ce7a5-4818-7c21-a68e-472133272780" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PrivateDebtMember_019ce7a5-4818-7646-8a1e-bfa5c7295760" xlink:href="jrvr-20260331.xsd#jrvr_PrivateDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-7aa9-a796-a81d2d47b9a9" xlink:to="loc_jrvr_PrivateDebtMember_019ce7a5-4818-7646-8a1e-bfa5c7295760" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PrivateSpecialityCreditMember_019ce7a5-4818-7434-a17b-2cf140b971dc" xlink:href="jrvr-20260331.xsd#jrvr_PrivateSpecialityCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_PrivateDebtMember_019ce7a5-4818-7646-8a1e-bfa5c7295760" xlink:to="loc_jrvr_PrivateSpecialityCreditMember_019ce7a5-4818-7434-a17b-2cf140b971dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PrivateSpecialtyCreditMember_019d42e1-9426-74c2-8855-8e2c7ef4f76f" xlink:href="jrvr-20260331.xsd#jrvr_PrivateSpecialtyCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019ce7a5-4818-7aa9-a796-a81d2d47b9a9" xlink:to="loc_jrvr_PrivateSpecialtyCreditMember_019d42e1-9426-74c2-8855-8e2c7ef4f76f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ce7a5-4818-78b3-ad93-f0e1b297862f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:to="loc_srt_RangeAxis_019ce7a5-4818-78b3-ad93-f0e1b297862f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce7a5-4818-78b3-ad93-f0e1b297862f_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ce7a5-4818-78b3-ad93-f0e1b297862f" xlink:to="loc_srt_RangeMember_019ce7a5-4818-78b3-ad93-f0e1b297862f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ce7a5-4818-75fe-9ff1-f25ca297dfdb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ce7a5-4818-78b3-ad93-f0e1b297862f" xlink:to="loc_srt_RangeMember_019ce7a5-4818-75fe-9ff1-f25ca297dfdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ce7a5-4818-7a46-a1de-9d56d3ad2912" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ce7a5-4818-75fe-9ff1-f25ca297dfdb" xlink:to="loc_srt_MinimumMember_019ce7a5-4818-7a46-a1de-9d56d3ad2912" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ce7a5-4818-79a4-a64c-b3b9bf50beff" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ce7a5-4818-75fe-9ff1-f25ca297dfdb" xlink:to="loc_srt_MaximumMember_019ce7a5-4818-79a4-a64c-b3b9bf50beff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-74ba-ad7b-49d096943060" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-74ba-ad7b-49d096943060" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-74ba-ad7b-49d096943060_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-74ba-ad7b-49d096943060" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-74ba-ad7b-49d096943060_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4818-74ba-ad7b-49d096943060" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_InvestmentInLlcMember_019ce7a5-4818-7c37-9237-7c27489a1791" xlink:href="jrvr-20260331.xsd#jrvr_InvestmentInLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_InvestmentInLlcMember_019ce7a5-4818-7c37-9237-7c27489a1791" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableOneMember_019ce7a5-4818-7a7c-8414-76a332b95ba3" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivableOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_NotesReceivableOneMember_019ce7a5-4818-7a7c-8414-76a332b95ba3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableTwoMember_019ce7a5-4818-743c-9def-a47719f35e11" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivableTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_NotesReceivableTwoMember_019ce7a5-4818-743c-9def-a47719f35e11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableThreeMember_019ce7a5-4818-7088-b4e2-2b284558a880" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivableThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_NotesReceivableThreeMember_019ce7a5-4818-7088-b4e2-2b284558a880" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableFourMember_019ce7a5-4818-7cbc-98cf-c08b9db1c6c4" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivableFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_NotesReceivableFourMember_019ce7a5-4818-7cbc-98cf-c08b9db1c6c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableFiveMember_019d42de-a7e7-78c8-ad72-ad35a82e4d99" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivableFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_NotesReceivableFiveMember_019d42de-a7e7-78c8-ad72-ad35a82e4d99" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableSixMember_019d42de-a7e8-7c1a-81de-e6ceff6a4119" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivableSixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_NotesReceivableSixMember_019d42de-a7e8-7c1a-81de-e6ceff6a4119" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivableSevenMember_019d42de-a7e8-7eb4-811e-112739547844" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivableSevenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4818-759c-a67c-ffc4b4cc4a61" xlink:to="loc_jrvr_NotesReceivableSevenMember_019d42de-a7e8-7eb4-811e-112739547844" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce7a5-4818-74ce-93a2-83d94af4c115" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce7a5-4818-74ce-93a2-83d94af4c115" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ce7a5-4818-74ce-93a2-83d94af4c115_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce7a5-4818-74ce-93a2-83d94af4c115" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ce7a5-4818-74ce-93a2-83d94af4c115_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ce7a5-4818-793f-9377-3b8212b2aac1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ce7a5-4818-74ce-93a2-83d94af4c115" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ce7a5-4818-793f-9377-3b8212b2aac1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_VariousLLCsMember_019ce7a5-4818-766c-b9d7-4f60b16eb163" xlink:href="jrvr-20260331.xsd#jrvr_VariousLLCsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ce7a5-4818-793f-9377-3b8212b2aac1" xlink:to="loc_jrvr_VariousLLCsMember_019ce7a5-4818-766c-b9d7-4f60b16eb163" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019d42de-a7e8-7b55-89e1-7e14082339a6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019ce7a5-4818-7e5f-914e-b6ef3ea337f4" xlink:to="loc_srt_CounterpartyNameAxis_019d42de-a7e8-7b55-89e1-7e14082339a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019d42de-a7e8-7b55-89e1-7e14082339a6_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019d42de-a7e8-7b55-89e1-7e14082339a6" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019d42de-a7e8-7b55-89e1-7e14082339a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019d42de-a7e8-7ef6-ac62-4edda913ea38" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019d42de-a7e8-7b55-89e1-7e14082339a6" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019d42de-a7e8-7ef6-ac62-4edda913ea38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_TPGAngeloGordonMember_019ddaba-4ebf-7a46-ad90-fa28463d94a7" xlink:href="jrvr-20260331.xsd#jrvr_TPGAngeloGordonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019d42de-a7e8-7ef6-ac62-4edda913ea38" xlink:to="loc_jrvr_TPGAngeloGordonMember_019ddaba-4ebf-7a46-ad90-fa28463d94a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SixthStreetMember_019d42de-a7e8-71e9-8956-47d6d9a64cee" xlink:href="jrvr-20260331.xsd#jrvr_SixthStreetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019d42de-a7e8-7ef6-ac62-4edda913ea38" xlink:to="loc_jrvr_SixthStreetMember_019d42de-a7e8-71e9-8956-47d6d9a64cee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInvestments_019ce7a5-4818-70e7-b8dd-3f9ea6cbdb91" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_us-gaap_OtherInvestments_019ce7a5-4818-70e7-b8dd-3f9ea6cbdb91" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019ce7a5-4818-726e-ab88-ad96262d131a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019ce7a5-4818-726e-ab88-ad96262d131a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeNet_019ce7a5-4818-796c-aa1c-17e22135f4c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentIncomeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_us-gaap_InvestmentIncomeNet_019ce7a5-4818-796c-aa1c-17e22135f4c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019d42de-a7e8-7910-a5f0-2f3a9916bc7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019d42de-a7e8-7910-a5f0-2f3a9916bc7f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentDividendsOrDistributions_019d42de-a7e8-711c-9152-a34437ad3b05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentDividendsOrDistributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_us-gaap_EquityMethodInvestmentDividendsOrDistributions_019d42de-a7e8-711c-9152-a34437ad3b05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommitmentToInvestmentInLimitedPartnership_019d42de-a7e8-7f48-930e-b40c5f0bd6cf" xlink:href="jrvr-20260331.xsd#jrvr_CommitmentToInvestmentInLimitedPartnership"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_jrvr_CommitmentToInvestmentInLimitedPartnership_019d42de-a7e8-7f48-930e-b40c5f0bd6cf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfNotesIssued_019d42de-a7e8-78a9-bece-18cdf7ae1860" xlink:href="jrvr-20260331.xsd#jrvr_NumberOfNotesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_jrvr_NumberOfNotesIssued_019d42de-a7e8-78a9-bece-18cdf7ae1860" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfNotesMaturingIn2031_019ddf60-4be8-7a31-877d-d0168364fd25" xlink:href="jrvr-20260331.xsd#jrvr_NumberOfNotesMaturingIn2031"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_jrvr_NumberOfNotesMaturingIn2031_019ddf60-4be8-7a31-877d-d0168364fd25" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRate_019d42de-a7e8-791a-b2b1-09a55728a1fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_us-gaap_InvestmentInterestRate_019d42de-a7e8-791a-b2b1-09a55728a1fc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfNotesMaturingIn2035_019ddf61-d947-7940-9af7-2c12afd45f22" xlink:href="jrvr-20260331.xsd#jrvr_NumberOfNotesMaturingIn2035"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_jrvr_NumberOfNotesMaturingIn2035_019ddf61-d947-7940-9af7-2c12afd45f22" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NumberOfNotesMaturingIn2064_019ddf62-8616-7d90-8318-3acdbea3ca96" xlink:href="jrvr-20260331.xsd#jrvr_NumberOfNotesMaturingIn2064"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_jrvr_NumberOfNotesMaturingIn2064_019ddf62-8616-7d90-8318-3acdbea3ca96" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommitmentToInvestInNotesReceivable_019d42e1-9426-77db-ae19-5040749d97e8" xlink:href="jrvr-20260331.xsd#jrvr_CommitmentToInvestInNotesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019ce7a5-4818-7e66-834e-4e3c9677602b" xlink:to="loc_jrvr_CommitmentToInvestInNotesReceivable_019d42e1-9426-77db-ae19-5040749d97e8" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/GoodwillandIntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-73e3-a852-9236a9258cc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ce7a5-4818-70d6-883f-8bc1addb6212" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ce7a5-4818-73e3-a852-9236a9258cc2" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ce7a5-4818-70d6-883f-8bc1addb6212" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ce7a5-4818-7076-ab13-e5218f24f765" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019ce7a5-4818-70d6-883f-8bc1addb6212" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ce7a5-4818-7076-ab13-e5218f24f765" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ce7a5-4818-7076-ab13-e5218f24f765_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ce7a5-4818-7076-ab13-e5218f24f765" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ce7a5-4818-7076-ab13-e5218f24f765_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ce7a5-4818-766c-aa0f-06774f5263e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ce7a5-4818-7076-ab13-e5218f24f765" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ce7a5-4818-766c-aa0f-06774f5263e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_JamesRiverGroupIncMember_019ce7a5-4818-71f1-9c06-7ac95cbeeca8" xlink:href="jrvr-20260331.xsd#jrvr_JamesRiverGroupIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ce7a5-4818-766c-aa0f-06774f5263e8" xlink:to="loc_jrvr_JamesRiverGroupIncMember_019ce7a5-4818-71f1-9c06-7ac95cbeeca8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019ce7a5-4818-7f30-bdc9-8e33538c708d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ce7a5-4818-73e3-a852-9236a9258cc2" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019ce7a5-4818-7f30-bdc9-8e33538c708d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019ce7a5-4818-72c0-8625-9f9baac4bee9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019ce7a5-4818-73e3-a852-9236a9258cc2" xlink:to="loc_us-gaap_Goodwill_019ce7a5-4818-72c0-8625-9f9baac4bee9" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/GoodwillandIntangibleAssetsScheduleofGoodwillandIntangibleAssetsDetails" xlink:type="simple" xlink:href="jrvr-20260331.xsd#GoodwillandIntangibleAssetsScheduleofGoodwillandIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/GoodwillandIntangibleAssetsScheduleofGoodwillandIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AcquiredIntangibleAssetsLineItems_019ce7a5-4818-72fd-ad2b-0ea2aa14a9c7" xlink:href="jrvr-20260331.xsd#jrvr_AcquiredIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_019ce7a5-4818-73a7-8f19-9c57e8cfacff" xlink:href="jrvr-20260331.xsd#jrvr_ScheduleOfAcquiredIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_019ce7a5-4818-72fd-ad2b-0ea2aa14a9c7" xlink:to="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_019ce7a5-4818-73a7-8f19-9c57e8cfacff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7ea1-b228-7b664d236095" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_019ce7a5-4818-73a7-8f19-9c57e8cfacff" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7ea1-b228-7b664d236095" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-7ea1-b228-7b664d236095_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7ea1-b228-7b664d236095" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-7ea1-b228-7b664d236095_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-766f-a543-3264ae487c9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7ea1-b228-7b664d236095" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-766f-a543-3264ae487c9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksMember_019ce7a5-4818-7e44-9e96-1323f41134a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-766f-a543-3264ae487c9a" xlink:to="loc_us-gaap_TrademarksMember_019ce7a5-4818-7e44-9e96-1323f41134a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicensingAgreementsMember_019ce7a5-4818-7f4e-9148-9be7c3ba182b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LicensingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-766f-a543-3264ae487c9a" xlink:to="loc_us-gaap_LicensingAgreementsMember_019ce7a5-4818-7f4e-9148-9be7c3ba182b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7c73-b7ff-cc0b194592af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ScheduleOfAcquiredIntangibleAssetsTable_019ce7a5-4818-73a7-8f19-9c57e8cfacff" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7c73-b7ff-cc0b194592af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-7c73-b7ff-cc0b194592af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7c73-b7ff-cc0b194592af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-7c73-b7ff-cc0b194592af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-72a6-be6e-727149882034" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ce7a5-4818-7c73-b7ff-cc0b194592af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-72a6-be6e-727149882034" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_BrokerRelationshipsMember_019ce7a5-4818-7663-a5bd-ca6a57d79518" xlink:href="jrvr-20260331.xsd#jrvr_BrokerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ce7a5-4818-72a6-be6e-727149882034" xlink:to="loc_jrvr_BrokerRelationshipsMember_019ce7a5-4818-7663-a5bd-ca6a57d79518" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019ce7a5-4818-796a-bc42-031b846d8f31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_019ce7a5-4818-72fd-ad2b-0ea2aa14a9c7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019ce7a5-4818-796a-bc42-031b846d8f31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019ce7a5-4818-74f0-998a-ed0530221fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_019ce7a5-4818-72fd-ad2b-0ea2aa14a9c7" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019ce7a5-4818-74f0-998a-ed0530221fd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ce7a5-4818-7e96-a9f1-a95ecac670cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_019ce7a5-4818-72fd-ad2b-0ea2aa14a9c7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ce7a5-4818-7e96-a9f1-a95ecac670cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ce7a5-4818-7184-ae2a-a9d5bda3de75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ce7a5-4818-7e96-a9f1-a95ecac670cc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ce7a5-4818-7184-ae2a-a9d5bda3de75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ce7a5-4818-7e00-ac50-baa99e57772f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_019ce7a5-4818-7e96-a9f1-a95ecac670cc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ce7a5-4818-7e00-ac50-baa99e57772f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019ce7a5-4818-7f9a-800f-80e32cdbe099" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AcquiredIntangibleAssetsLineItems_019ce7a5-4818-72fd-ad2b-0ea2aa14a9c7" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019ce7a5-4818-7f9a-800f-80e32cdbe099" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/EarningsPerShareNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20260331.xsd#EarningsPerShareNarrativeDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/EarningsPerShareNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce7a5-4818-7f51-835e-b83c41fa2636" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce7a5-4818-7059-b2b9-4c7321bf7f01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce7a5-4818-7f51-835e-b83c41fa2636" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce7a5-4818-7059-b2b9-4c7321bf7f01" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce7a5-4818-708f-a92d-9e5a25f5cfac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce7a5-4818-7059-b2b9-4c7321bf7f01" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce7a5-4818-708f-a92d-9e5a25f5cfac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce7a5-4818-708f-a92d-9e5a25f5cfac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce7a5-4818-708f-a92d-9e5a25f5cfac" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce7a5-4818-708f-a92d-9e5a25f5cfac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce7a5-4818-71dd-99d3-ca8346a5ac6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ce7a5-4818-708f-a92d-9e5a25f5cfac" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce7a5-4818-71dd-99d3-ca8346a5ac6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019d8a5d-c167-701c-8b01-6afd38ffc5be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce7a5-4818-71dd-99d3-ca8346a5ac6a" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019d8a5d-c167-701c-8b01-6afd38ffc5be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_019d8a5e-1d20-7cde-b337-db4810dd36e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ce7a5-4818-71dd-99d3-ca8346a5ac6a" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_019d8a5e-1d20-7cde-b337-db4810dd36e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ddacb-e973-78a4-847f-4f46677a2150" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce7a5-4818-7059-b2b9-4c7321bf7f01" xlink:to="loc_us-gaap_AwardTypeAxis_019ddacb-e973-78a4-847f-4f46677a2150" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddacb-e973-78a4-847f-4f46677a2150_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ddacb-e973-78a4-847f-4f46677a2150" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddacb-e973-78a4-847f-4f46677a2150_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddacb-e973-7bdf-987e-37812019df1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ddacb-e973-78a4-847f-4f46677a2150" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddacb-e973-7bdf-987e-37812019df1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ddacc-042a-7065-9889-39bd3b7b54d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddacb-e973-7bdf-987e-37812019df1b" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ddacc-042a-7065-9889-39bd3b7b54d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ddacc-51b9-72c1-b71d-15778a399892" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ce7a5-4818-7059-b2b9-4c7321bf7f01" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ddacc-51b9-72c1-b71d-15778a399892" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ddacc-51b9-72c1-b71d-15778a399892_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ddacc-51b9-72c1-b71d-15778a399892" xlink:to="loc_us-gaap_ClassOfStockDomain_019ddacc-51b9-72c1-b71d-15778a399892_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ddacc-51b9-7c3c-a8ed-6a16c8133da6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ddacc-51b9-72c1-b71d-15778a399892" xlink:to="loc_us-gaap_ClassOfStockDomain_019ddacc-51b9-7c3c-a8ed-6a16c8133da6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_019ddacc-7d71-7252-bb14-250c534b0748" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ddacc-51b9-7c3c-a8ed-6a16c8133da6" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_019ddacc-7d71-7252-bb14-250c534b0748" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ce7a5-4818-77a0-94a1-146423bca8aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce7a5-4818-7f51-835e-b83c41fa2636" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ce7a5-4818-77a0-94a1-146423bca8aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019ddac9-9ff0-7a02-ba17-1c13e80fbdd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce7a5-4818-7f51-835e-b83c41fa2636" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019ddac9-9ff0-7a02-ba17-1c13e80fbdd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock_019ddaca-21f3-7f8f-9b5a-16a34aa63529" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ce7a5-4818-7f51-835e-b83c41fa2636" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock_019ddaca-21f3-7f8f-9b5a-16a34aa63529" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesNarrativeDetails" xlink:type="simple" xlink:href="jrvr-20260331.xsd#ReserveforLossesandLossAdjustmentExpensesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:href="jrvr-20260331.xsd#jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_019ce7a5-4818-7272-83b0-b2ff04ae417a" xlink:href="jrvr-20260331.xsd#jrvr_ReserveForLossesAndLossAdjustmentExpensesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_019ce7a5-4818-7272-83b0-b2ff04ae417a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019d42a9-d347-71ca-955b-157cf0518c06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_019ce7a5-4818-7272-83b0-b2ff04ae417a" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019d42a9-d347-71ca-955b-157cf0518c06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d42a9-d347-71ca-955b-157cf0518c06_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d42a9-d347-71ca-955b-157cf0518c06" xlink:to="loc_us-gaap_SegmentDomain_019d42a9-d347-71ca-955b-157cf0518c06_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019d42a9-d347-740e-ad17-84e154b512a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019d42a9-d347-71ca-955b-157cf0518c06" xlink:to="loc_us-gaap_SegmentDomain_019d42a9-d347-740e-ad17-84e154b512a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_019d42a9-d347-7bef-9c27-46d63943bea7" xlink:href="jrvr-20260331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d42a9-d347-740e-ad17-84e154b512a4" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_019d42a9-d347-7bef-9c27-46d63943bea7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SpecialtyAdmittedInsuranceMember_019d42a9-d347-743f-a91c-bd8d42ed066b" xlink:href="jrvr-20260331.xsd#jrvr_SpecialtyAdmittedInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019d42a9-d347-740e-ad17-84e154b512a4" xlink:to="loc_jrvr_SpecialtyAdmittedInsuranceMember_019d42a9-d347-743f-a91c-bd8d42ed066b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_019d42a9-f81a-7c14-816a-27c2a0441d83" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_019ce7a5-4818-7272-83b0-b2ff04ae417a" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_019d42a9-f81a-7c14-816a-27c2a0441d83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019d42a9-f81a-7c14-816a-27c2a0441d83_default" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019d42a9-f81a-7c14-816a-27c2a0441d83" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019d42a9-f81a-7c14-816a-27c2a0441d83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019d42a9-f81a-7580-abbe-7fa9996d11b5" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019d42a9-f81a-7c14-816a-27c2a0441d83" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019d42a9-f81a-7580-abbe-7fa9996d11b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoLPTMember_019ddad2-5c1a-73b6-953f-59704facf8e9" xlink:href="jrvr-20260331.xsd#jrvr_CommercialAutoLPTMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_019d42a9-f81a-7580-abbe-7fa9996d11b5" xlink:to="loc_jrvr_CommercialAutoLPTMember_019ddad2-5c1a-73b6-953f-59704facf8e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ESADCAgreementMember_019d42a9-f81a-74c9-bf3f-76f01736dc3b" xlink:href="jrvr-20260331.xsd#jrvr_ESADCAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_019d42a9-f81a-7580-abbe-7fa9996d11b5" xlink:to="loc_jrvr_ESADCAgreementMember_019d42a9-f81a-74c9-bf3f-76f01736dc3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ESTopUpADCMember_019d42a9-f81a-78e9-bbec-ee34acca7135" xlink:href="jrvr-20260331.xsd#jrvr_ESTopUpADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_019d42a9-f81a-7580-abbe-7fa9996d11b5" xlink:to="loc_jrvr_ESTopUpADCMember_019d42a9-f81a-78e9-bbec-ee34acca7135" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019d42a9-f81a-7d2a-8397-65ae1ec3b76a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_019ce7a5-4818-7272-83b0-b2ff04ae417a" xlink:to="loc_us-gaap_SubsegmentsAxis_019d42a9-f81a-7d2a-8397-65ae1ec3b76a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019d42a9-f81a-7d2a-8397-65ae1ec3b76a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019d42a9-f81a-7d2a-8397-65ae1ec3b76a" xlink:to="loc_us-gaap_SubsegmentsDomain_019d42a9-f81a-7d2a-8397-65ae1ec3b76a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019d42a9-f81a-7e42-8dda-5cd66d3d2d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019d42a9-f81a-7d2a-8397-65ae1ec3b76a" xlink:to="loc_us-gaap_SubsegmentsDomain_019d42a9-f81a-7e42-8dda-5cd66d3d2d4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoBusinessMember_019d42a9-f81a-7a7d-bc1e-ecdd12070902" xlink:href="jrvr-20260331.xsd#jrvr_CommercialAutoBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019d42a9-f81a-7e42-8dda-5cd66d3d2d4e" xlink:to="loc_jrvr_CommercialAutoBusinessMember_019d42a9-f81a-7a7d-bc1e-ecdd12070902" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019d42a9-f81a-7ee2-bdef-9c7721e58ff6" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesTable_019ce7a5-4818-7272-83b0-b2ff04ae417a" xlink:to="loc_dei_LegalEntityAxis_019d42a9-f81a-7ee2-bdef-9c7721e58ff6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019d42a9-f81a-7ee2-bdef-9c7721e58ff6_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019d42a9-f81a-7ee2-bdef-9c7721e58ff6" xlink:to="loc_dei_EntityDomain_019d42a9-f81a-7ee2-bdef-9c7721e58ff6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019d42a9-f81a-7653-bb08-e85b4d2d6c48" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019d42a9-f81a-7ee2-bdef-9c7721e58ff6" xlink:to="loc_dei_EntityDomain_019d42a9-f81a-7653-bb08-e85b4d2d6c48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_StateNationalMember_019d42a9-f81a-7c8b-aa33-127b4b8a6aa3" xlink:href="jrvr-20260331.xsd#jrvr_StateNationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019d42a9-f81a-7653-bb08-e85b4d2d6c48" xlink:to="loc_jrvr_StateNationalMember_019d42a9-f81a-7c8b-aa33-127b4b8a6aa3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_019d42a9-b77b-71ad-bf09-6484c04b4f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_019d42a9-b77b-71ad-bf09-6484c04b4f8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019d42a9-d347-7c96-be5f-0afd4b3c78bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019d42a9-d347-7c96-be5f-0afd4b3c78bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CumulativeAmountsCededUnderLossPortfolioTransfer_019d42a9-f81a-7647-a3ca-7caa2b0d5cd2" xlink:href="jrvr-20260331.xsd#jrvr_CumulativeAmountsCededUnderLossPortfolioTransfer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_jrvr_CumulativeAmountsCededUnderLossPortfolioTransfer_019d42a9-f81a-7647-a3ca-7caa2b0d5cd2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage_019d42a9-f81a-7f8f-bdca-b60c51f46805" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyReinsuredRiskPercentage_019d42a9-f81a-7f8f-bdca-b60c51f46805" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsureExcessAmount_019d42a9-f81a-7e6c-b9d0-b3c53a42bdce" xlink:href="jrvr-20260331.xsd#jrvr_ReinsureExcessAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_jrvr_ReinsureExcessAmount_019d42a9-f81a-7e6c-b9d0-b3c53a42bdce" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceAggregateCoverageLimit_019d42a9-f81a-7486-917b-33d4eba9f6af" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceAggregateCoverageLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_jrvr_ReinsuranceAggregateCoverageLimit_019d42a9-f81a-7486-917b-33d4eba9f6af" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForReinsurance_019d42a9-f81a-73f3-82cd-0e1a2b26a692" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_us-gaap_PaymentsForReinsurance_019d42a9-f81a-73f3-82cd-0e1a2b26a692" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019d42a9-f81a-71ac-81c4-6ef840e66331" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019d42a9-f81a-71ac-81c4-6ef840e66331" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceAggregateCoverageLimitAmountRemaining_019d42a9-f81a-70e7-ab40-cbecbd7e2e6d" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceAggregateCoverageLimitAmountRemaining"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_jrvr_ReinsuranceAggregateCoverageLimitAmountRemaining_019d42a9-f81a-70e7-ab40-cbecbd7e2e6d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ddad0-1bf0-7049-81c2-14215f7ec101" xlink:href="jrvr-20260331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReserveForLossesAndLossAdjustmentExpensesLineItems_019ce7a5-4818-7443-8d2c-c7ce33195306" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ddad0-1bf0-7049-81c2-14215f7ec101" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesReserveforLossesandLossAdjustmentExpensesNetofReinsuranceDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-7ce0-b1ed-3f6389c72127" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7209-a381-0a6d542251cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_019ce7a5-4818-7ce0-b1ed-3f6389c72127" xlink:to="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7209-a381-0a6d542251cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a41-9b15-744d1f0d9473" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7209-a381-0a6d542251cf" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a41-9b15-744d1f0d9473" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7a41-9b15-744d1f0d9473_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a41-9b15-744d1f0d9473" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7a41-9b15-744d1f0d9473_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7210-b496-b2d5ab1cda8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a41-9b15-744d1f0d9473" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7210-b496-b2d5ab1cda8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-7302-a8a6-f99007bbb9e7" xlink:href="jrvr-20260331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-7210-b496-b2d5ab1cda8e" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-7302-a8a6-f99007bbb9e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_019ce7a5-4818-7ce0-b1ed-3f6389c72127" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_019ce7a5-4818-7f6b-a26b-51b268848c57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_019ce7a5-4818-7f6b-a26b-51b268848c57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_019ce7a5-4818-7124-a42c-f631660834de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_019ce7a5-4818-7124-a42c-f631660834de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019ce7a5-4818-7df9-b350-b04f7e8d0ca9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_019ce7a5-4818-7124-a42c-f631660834de" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019ce7a5-4818-7df9-b350-b04f7e8d0ca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ce7a5-4818-74c5-87e5-0b4aef407c95" xlink:href="jrvr-20260331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_019ce7a5-4818-7124-a42c-f631660834de" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ce7a5-4818-74c5-87e5-0b4aef407c95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019ce7a5-4818-7133-9bca-35499f1598c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_019ce7a5-4818-7124-a42c-f631660834de" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019ce7a5-4818-7133-9bca-35499f1598c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019ce7a5-4818-7e1f-942f-c8c1b43de9f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract_019ce7a5-4818-7124-a42c-f631660834de" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019ce7a5-4818-7e1f-942f-c8c1b43de9f3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_019ce7a5-4818-7a96-adb6-8c70f110db3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_019ce7a5-4818-7a96-adb6-8c70f110db3f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1_019ce7a5-4818-78e8-a2c9-46f7a90d2926" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_019ce7a5-4818-7a96-adb6-8c70f110db3f" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1_019ce7a5-4818-78e8-a2c9-46f7a90d2926" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1_019ce7a5-4818-7b61-80ec-9608a2c86b99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_019ce7a5-4818-7a96-adb6-8c70f110db3f" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1_019ce7a5-4818-7b61-80ec-9608a2c86b99" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLossesAndLossAdjustmentExpense_019ce7a5-4818-7304-97e9-ec4105fb7bb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForLossesAndLossAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract_019ce7a5-4818-7a96-adb6-8c70f110db3f" xlink:to="loc_us-gaap_PaymentsForLossesAndLossAdjustmentExpense_019ce7a5-4818-7304-97e9-ec4105fb7bb7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_IncreaseDecreaseInDeferredReinsuranceGain_019ce7a5-4818-7367-9086-bd6d2f98bd9c" xlink:href="jrvr-20260331.xsd#jrvr_IncreaseDecreaseInDeferredReinsuranceGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:to="loc_jrvr_IncreaseDecreaseInDeferredReinsuranceGain_019ce7a5-4818-7367-9086-bd6d2f98bd9c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_019ce7a5-4818-716c-a2d2-63e3ff84aeb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesGross_019ce7a5-4818-767b-923a-29348d828c65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReinsuranceRecoverablesOnUnpaidLossesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:to="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesGross_019ce7a5-4818-767b-923a-29348d828c65" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_019ce7a5-4818-7a07-9147-ec493b397240" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_019ce7a5-4818-73fe-8a4b-bcd76351e764" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_019ce7a5-4818-7a07-9147-ec493b397240" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ReserveforLossesandLossAdjustmentExpensesRetroactiveReinsuranceDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-7711-8bc4-43a9b6859dbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7e25-9b69-7a44fde034a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_019ce7a5-4818-7711-8bc4-43a9b6859dbd" xlink:to="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7e25-9b69-7a44fde034a1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-716a-bdd3-ef741da7d05a" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7e25-9b69-7a44fde034a1" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-716a-bdd3-ef741da7d05a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-716a-bdd3-ef741da7d05a_default" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-716a-bdd3-ef741da7d05a" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-716a-bdd3-ef741da7d05a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7e5c-8324-53a40f05d785" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-716a-bdd3-ef741da7d05a" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7e5c-8324-53a40f05d785" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoLPTESADCAndESTopUpADCMember_019de414-f50f-7e35-8b3d-d759799bb3c4" xlink:href="jrvr-20260331.xsd#jrvr_CommercialAutoLPTESADCAndESTopUpADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7e5c-8324-53a40f05d785" xlink:to="loc_jrvr_CommercialAutoLPTESADCAndESTopUpADCMember_019de414-f50f-7e35-8b3d-d759799bb3c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoLPTMember_019ddace-400c-76a7-a2bd-8003be36e321" xlink:href="jrvr-20260331.xsd#jrvr_CommercialAutoLPTMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_CommercialAutoLPTESADCAndESTopUpADCMember_019de414-f50f-7e35-8b3d-d759799bb3c4" xlink:to="loc_jrvr_CommercialAutoLPTMember_019ddace-400c-76a7-a2bd-8003be36e321" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ESADCAgreementMember_019ce7a5-4818-7f38-9cdd-bb58c72f2b71" xlink:href="jrvr-20260331.xsd#jrvr_ESADCAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_CommercialAutoLPTESADCAndESTopUpADCMember_019de414-f50f-7e35-8b3d-d759799bb3c4" xlink:to="loc_jrvr_ESADCAgreementMember_019ce7a5-4818-7f38-9cdd-bb58c72f2b71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ESTopUpADCMember_019d65c0-8117-729a-9463-7cca4065ad82" xlink:href="jrvr-20260331.xsd#jrvr_ESTopUpADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_CommercialAutoLPTESADCAndESTopUpADCMember_019de414-f50f-7e35-8b3d-d759799bb3c4" xlink:to="loc_jrvr_ESTopUpADCMember_019d65c0-8117-729a-9463-7cca4065ad82" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-72b6-88ca-71a020648fe3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7e25-9b69-7a44fde034a1" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-72b6-88ca-71a020648fe3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-72b6-88ca-71a020648fe3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-72b6-88ca-71a020648fe3" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-72b6-88ca-71a020648fe3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7c58-ba7d-e9e2825d861e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-72b6-88ca-71a020648fe3" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7c58-ba7d-e9e2825d861e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-74b0-a325-c406d3c2f2a9" xlink:href="jrvr-20260331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-7c58-ba7d-e9e2825d861e" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-74b0-a325-c406d3c2f2a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d83-905b-6ff51b4b2e96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTable_019ce7a5-4818-7e25-9b69-7a44fde034a1" xlink:to="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d83-905b-6ff51b4b2e96" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-7d83-905b-6ff51b4b2e96_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d83-905b-6ff51b4b2e96" xlink:to="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-7d83-905b-6ff51b4b2e96_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-755f-879f-dea11346f880" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d83-905b-6ff51b4b2e96" xlink:to="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-755f-879f-dea11346f880" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoBusinessMember_019ce7a5-4818-7725-8507-32c003492942" xlink:href="jrvr-20260331.xsd#jrvr_CommercialAutoBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-755f-879f-dea11346f880" xlink:to="loc_jrvr_CommercialAutoBusinessMember_019ce7a5-4818-7725-8507-32c003492942" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DeferredReinsuranceGain_019ce7a5-4818-7179-9823-946987f7e8b5" xlink:href="jrvr-20260331.xsd#jrvr_DeferredReinsuranceGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_019ce7a5-4818-7711-8bc4-43a9b6859dbd" xlink:to="loc_jrvr_DeferredReinsuranceGain_019ce7a5-4818-7179-9823-946987f7e8b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019dd5df-06ba-702c-9938-511e6ecbfa0b" xlink:href="jrvr-20260331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_019ce7a5-4818-7711-8bc4-43a9b6859dbd" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019dd5df-06ba-702c-9938-511e6ecbfa0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RetroactiveReinsuranceBenefitRecognized_019ce7a5-4818-7907-957e-add686d9e918" xlink:href="jrvr-20260331.xsd#jrvr_RetroactiveReinsuranceBenefitRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityLineItems_019ce7a5-4818-7711-8bc4-43a9b6859dbd" xlink:to="loc_jrvr_RetroactiveReinsuranceBenefitRecognized_019ce7a5-4818-7907-957e-add686d9e918" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_DeferredReinsuranceGain_019ce7a5-4818-712c-9ca6-5522dafeade9" xlink:href="jrvr-20260331.xsd#jrvr_DeferredReinsuranceGain"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/ContingentLiabilitiesDetails" xlink:type="simple" xlink:href="jrvr-20260331.xsd#ContingentLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://jrgh.net/role/ContingentLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ContingentLiabilitiesLineItems_019ce7a5-4818-7c81-aa22-bf3e3bb5bdd7" xlink:href="jrvr-20260331.xsd#jrvr_ContingentLiabilitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ContingentLiabilitiesTable_019ce7a5-4818-7014-8bf9-0898e6f6138a" xlink:href="jrvr-20260331.xsd#jrvr_ContingentLiabilitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_019ce7a5-4818-7c81-aa22-bf3e3bb5bdd7" xlink:to="loc_jrvr_ContingentLiabilitiesTable_019ce7a5-4818-7014-8bf9-0898e6f6138a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-7800-86e1-468dd9eeebb9" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_019ce7a5-4818-7014-8bf9-0898e6f6138a" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-7800-86e1-468dd9eeebb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7800-86e1-468dd9eeebb9_default" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-7800-86e1-468dd9eeebb9" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7800-86e1-468dd9eeebb9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7a31-9c6f-119963a6a4ad" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4818-7800-86e1-468dd9eeebb9" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7a31-9c6f-119963a6a4ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LossPortfolioTransferMember_019ce7a5-4818-7581-8570-5f98804eb037" xlink:href="jrvr-20260331.xsd#jrvr_LossPortfolioTransferMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4818-7a31-9c6f-119963a6a4ad" xlink:to="loc_jrvr_LossPortfolioTransferMember_019ce7a5-4818-7581-8570-5f98804eb037" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7067-bae7-9f702d481c97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_019ce7a5-4818-7014-8bf9-0898e6f6138a" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7067-bae7-9f702d481c97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7067-bae7-9f702d481c97_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7067-bae7-9f702d481c97" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7067-bae7-9f702d481c97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d1b-b5b4-306bad7009eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7067-bae7-9f702d481c97" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d1b-b5b4-306bad7009eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-7e31-80fd-71e284a430af" xlink:href="jrvr-20260331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d1b-b5b4-306bad7009eb" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-7e31-80fd-71e284a430af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d3c-a067-d3d3452e5709" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_019ce7a5-4818-7014-8bf9-0898e6f6138a" xlink:to="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d3c-a067-d3d3452e5709" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-7d3c-a067-d3d3452e5709_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d3c-a067-d3d3452e5709" xlink:to="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-7d3c-a067-d3d3452e5709_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-7b95-8c0c-b5d09df331e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019ce7a5-4818-7d3c-a067-d3d3452e5709" xlink:to="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-7b95-8c0c-b5d09df331e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoBusinessMember_019ce7a5-4818-7379-ac71-7b815d870892" xlink:href="jrvr-20260331.xsd#jrvr_CommercialAutoBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019ce7a5-4818-7b95-8c0c-b5d09df331e9" xlink:to="loc_jrvr_CommercialAutoBusinessMember_019ce7a5-4818-7379-ac71-7b815d870892" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019ce7a5-4818-7c4e-9b5d-bc7fb06f3780" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_019ce7a5-4818-7014-8bf9-0898e6f6138a" xlink:to="loc_srt_CounterpartyNameAxis_019ce7a5-4818-7c4e-9b5d-bc7fb06f3780" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce7a5-4818-7c4e-9b5d-bc7fb06f3780_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019ce7a5-4818-7c4e-9b5d-bc7fb06f3780" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce7a5-4818-7c4e-9b5d-bc7fb06f3780_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce7a5-4818-7cc3-9b7c-fb540fe8ecfd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019ce7a5-4818-7c4e-9b5d-bc7fb06f3780" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce7a5-4818-7cc3-9b7c-fb540fe8ecfd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AlekaMember_019ce7a5-4818-76a5-b24b-a3a23abf0522" xlink:href="jrvr-20260331.xsd#jrvr_AlekaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce7a5-4818-7cc3-9b7c-fb540fe8ecfd" xlink:to="loc_jrvr_AlekaMember_019ce7a5-4818-76a5-b24b-a3a23abf0522" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RasierMember_019ce7a5-4818-7346-be54-4cd2c5a9cc0d" xlink:href="jrvr-20260331.xsd#jrvr_RasierMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce7a5-4818-7cc3-9b7c-fb540fe8ecfd" xlink:to="loc_jrvr_RasierMember_019ce7a5-4818-7346-be54-4cd2c5a9cc0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RasierAndAlekaMember_019ce7a5-4818-749d-b0f3-15506845cb1a" xlink:href="jrvr-20260331.xsd#jrvr_RasierAndAlekaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019ce7a5-4818-7cc3-9b7c-fb540fe8ecfd" xlink:to="loc_jrvr_RasierAndAlekaMember_019ce7a5-4818-749d-b0f3-15506845cb1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssociatedTrustAgreementAxis_019ce7a5-4818-7e48-812b-c6760661879c" xlink:href="jrvr-20260331.xsd#jrvr_AssociatedTrustAgreementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_jrvr_ContingentLiabilitiesTable_019ce7a5-4818-7014-8bf9-0898e6f6138a" xlink:to="loc_jrvr_AssociatedTrustAgreementAxis_019ce7a5-4818-7e48-812b-c6760661879c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssociatedTrustAgreementDomain_019ce7a5-4818-7e48-812b-c6760661879c_default" xlink:href="jrvr-20260331.xsd#jrvr_AssociatedTrustAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_AssociatedTrustAgreementAxis_019ce7a5-4818-7e48-812b-c6760661879c" xlink:to="loc_jrvr_AssociatedTrustAgreementDomain_019ce7a5-4818-7e48-812b-c6760661879c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssociatedTrustAgreementDomain_019ce7a5-4818-7486-b5b6-7031e1a14b54" xlink:href="jrvr-20260331.xsd#jrvr_AssociatedTrustAgreementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_AssociatedTrustAgreementAxis_019ce7a5-4818-7e48-812b-c6760661879c" xlink:to="loc_jrvr_AssociatedTrustAgreementDomain_019ce7a5-4818-7486-b5b6-7031e1a14b54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_IndemnityTrustAndLossFundTrustMember_019ce7a5-4818-74cf-9d54-692f48b1489a" xlink:href="jrvr-20260331.xsd#jrvr_IndemnityTrustAndLossFundTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AssociatedTrustAgreementDomain_019ce7a5-4818-7486-b5b6-7031e1a14b54" xlink:to="loc_jrvr_IndemnityTrustAndLossFundTrustMember_019ce7a5-4818-74cf-9d54-692f48b1489a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LPTTrustAndLossFundTrustMember_019ce7a5-4818-7528-84ec-818560d9a25e" xlink:href="jrvr-20260331.xsd#jrvr_LPTTrustAndLossFundTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AssociatedTrustAgreementDomain_019ce7a5-4818-7486-b5b6-7031e1a14b54" xlink:to="loc_jrvr_LPTTrustAndLossFundTrustMember_019ce7a5-4818-7528-84ec-818560d9a25e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LossFundTrustMember_019ce7a5-4818-7e16-b391-6e832b07768d" xlink:href="jrvr-20260331.xsd#jrvr_LossFundTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_AssociatedTrustAgreementDomain_019ce7a5-4818-7486-b5b6-7031e1a14b54" xlink:to="loc_jrvr_LossFundTrustMember_019ce7a5-4818-7e16-b391-6e832b07768d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_019ce7a5-4818-7025-84cd-a0c54a127dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_019ce7a5-4818-7c81-aa22-bf3e3bb5bdd7" xlink:to="loc_us-gaap_ReinsuranceRecoverablesOnUnpaidLossesAllowance_019ce7a5-4818-7025-84cd-a0c54a127dc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RequiredCollateralPercentage_019ce7a5-4818-766c-a45a-1523c2c5790c" xlink:href="jrvr-20260331.xsd#jrvr_RequiredCollateralPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_019ce7a5-4818-7c81-aa22-bf3e3bb5bdd7" xlink:to="loc_jrvr_RequiredCollateralPercentage_019ce7a5-4818-766c-a45a-1523c2c5790c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CashEquivalentCollateralHeldInTrustArrangement_019ce7a5-4818-7fbe-8717-7b927359cec3" xlink:href="jrvr-20260331.xsd#jrvr_CashEquivalentCollateralHeldInTrustArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_019ce7a5-4818-7c81-aa22-bf3e3bb5bdd7" xlink:to="loc_jrvr_CashEquivalentCollateralHeldInTrustArrangement_019ce7a5-4818-7fbe-8717-7b927359cec3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRecoverablesGross_019ce7a5-4818-7b90-b520-39e3e1d370ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReinsuranceRecoverablesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ContingentLiabilitiesLineItems_019ce7a5-4818-7c81-aa22-bf3e3bb5bdd7" xlink:to="loc_us-gaap_ReinsuranceRecoverablesGross_019ce7a5-4818-7b90-b520-39e3e1d370ed" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SegmentInformationScheduleofSegmentResultsDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4818-723a-8a18-d172cac4d851" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4818-723a-8a18-d172cac4d851" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019ce7a5-4818-718e-a31d-21c374abb8d3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4818-723a-8a18-d172cac4d851" xlink:to="loc_srt_ConsolidationItemsAxis_019ce7a5-4818-718e-a31d-21c374abb8d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019ce7a5-4818-718e-a31d-21c374abb8d3_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019ce7a5-4818-718e-a31d-21c374abb8d3" xlink:to="loc_srt_ConsolidationItemsDomain_019ce7a5-4818-718e-a31d-21c374abb8d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019ce7a5-4818-70f3-92a2-4b6060cb1772" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019ce7a5-4818-718e-a31d-21c374abb8d3" xlink:to="loc_srt_ConsolidationItemsDomain_019ce7a5-4818-70f3-92a2-4b6060cb1772" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019ce7a5-4818-7e38-b9b9-871b515984cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019ce7a5-4818-70f3-92a2-4b6060cb1772" xlink:to="loc_us-gaap_OperatingSegmentsMember_019ce7a5-4818-7e38-b9b9-871b515984cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019ce7a5-4818-7d72-90dc-fef797bb42fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019ce7a5-4818-70f3-92a2-4b6060cb1772" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019ce7a5-4818-7d72-90dc-fef797bb42fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a09-8e85-2f415f21b1f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4818-723a-8a18-d172cac4d851" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a09-8e85-2f415f21b1f6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7a09-8e85-2f415f21b1f6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a09-8e85-2f415f21b1f6" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7a09-8e85-2f415f21b1f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d73-ad7e-20fae007f6b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4818-7a09-8e85-2f415f21b1f6" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d73-ad7e-20fae007f6b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-78f1-8cbd-cca2212b1ff5" xlink:href="jrvr-20260331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d73-ad7e-20fae007f6b2" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4818-78f1-8cbd-cca2212b1ff5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SpecialtyAdmittedInsuranceMember_019ce7a5-4818-7ae4-9195-568398721041" xlink:href="jrvr-20260331.xsd#jrvr_SpecialtyAdmittedInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d73-ad7e-20fae007f6b2" xlink:to="loc_jrvr_SpecialtyAdmittedInsuranceMember_019ce7a5-4818-7ae4-9195-568398721041" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019ce7a5-4818-7c52-a401-ec752675298d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4818-7d73-ad7e-20fae007f6b2" xlink:to="loc_us-gaap_CorporateAndOtherMember_019ce7a5-4818-7c52-a401-ec752675298d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsWrittenGross_019ce7a5-4818-7dac-9323-6106d804a152" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PremiumsWrittenGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_PremiumsWrittenGross_019ce7a5-4818-7dac-9323-6106d804a152" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsEarnedNet_019ce7a5-4818-7761-9816-889456465edd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PremiumsEarnedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_PremiumsEarnedNet_019ce7a5-4818-7761-9816-889456465edd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FeeIncome_019ce7a5-4818-78cc-865c-d6670d971d98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FeeIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_FeeIncome_019ce7a5-4818-78cc-865c-d6670d971d98" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019ce7a5-4818-76d7-aa3e-c85ac1bc48e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019ce7a5-4818-76d7-aa3e-c85ac1bc48e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ce7a5-4818-7781-a8bb-a51b46925f31" xlink:href="jrvr-20260331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ce7a5-4818-7781-a8bb-a51b46925f31" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseExcludingRetroactiveReinsurance_019ce7a5-4818-7cf1-bc85-ff1bb6de0a28" xlink:href="jrvr-20260331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseExcludingRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseExcludingRetroactiveReinsurance_019ce7a5-4818-7cf1-bc85-ff1bb6de0a28" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpensesAbstract_019ce7a5-4819-78b2-a157-89b91a5145c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingCostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_OperatingCostsAndExpensesAbstract_019ce7a5-4819-78b2-a157-89b91a5145c0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceCommissions_019ce7a5-4819-77a2-a168-c76cb37de3b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InsuranceCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019ce7a5-4819-78b2-a157-89b91a5145c0" xlink:to="loc_us-gaap_InsuranceCommissions_019ce7a5-4819-77a2-a168-c76cb37de3b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_019ce7a5-4819-7a44-a34e-33bd3f10dd12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019ce7a5-4819-78b2-a157-89b91a5145c0" xlink:to="loc_us-gaap_LaborAndRelatedExpense_019ce7a5-4819-7a44-a34e-33bd3f10dd12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_OtherOperatingExpenses_019ce7a5-4819-718f-b24e-35ae8149daa8" xlink:href="jrvr-20260331.xsd#jrvr_OtherOperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019ce7a5-4819-78b2-a157-89b91a5145c0" xlink:to="loc_jrvr_OtherOperatingExpenses_019ce7a5-4819-718f-b24e-35ae8149daa8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_019ce7a5-4819-70c8-8058-43324ddc6f43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_019ce7a5-4819-78b2-a157-89b91a5145c0" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_019ce7a5-4819-70c8-8058-43324ddc6f43" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_UnderwritingProfitLoss_019ce7a5-4819-7ee0-88ab-f54ac1ef533a" xlink:href="jrvr-20260331.xsd#jrvr_UnderwritingProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_jrvr_UnderwritingProfitLoss_019ce7a5-4819-7ee0-88ab-f54ac1ef533a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019ce7a5-4819-717a-bbff-fa06d6ee1f43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_Revenues_019ce7a5-4819-717a-bbff-fa06d6ee1f43" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019ce7a5-4819-7247-91bb-20823df8a4ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_NetInvestmentIncome_019ce7a5-4819-7247-91bb-20823df8a4ef" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_019ce7a5-4819-7978-bbf8-e694cf1e4dcf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_InterestExpense_019ce7a5-4819-7978-bbf8-e694cf1e4dcf" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019ce7a5-4819-7965-ae99-39d507d18398" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_us-gaap_Goodwill_019ce7a5-4819-7965-ae99-39d507d18398" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AssetsExcludingAssetsHeldForSale_019ce7a5-4819-775d-bdb1-e95dada00daf" xlink:href="jrvr-20260331.xsd#jrvr_AssetsExcludingAssetsHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4818-72b3-ba3d-d94cf91fd915" xlink:to="loc_jrvr_AssetsExcludingAssetsHeldForSale_019ce7a5-4819-775d-bdb1-e95dada00daf" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SegmentInformationReconciliationofOperatingSegmentsbyIndividualSegmentDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4819-7f82-8425-c00393368fe9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4819-7f82-8425-c00393368fe9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4819-7543-8210-89a8d75e84fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4819-7f82-8425-c00393368fe9" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4819-7543-8210-89a8d75e84fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4819-7543-8210-89a8d75e84fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4819-7543-8210-89a8d75e84fe" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4819-7543-8210-89a8d75e84fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ce7a5-4819-7eb5-9809-81bcd90b80da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ce7a5-4819-7543-8210-89a8d75e84fe" xlink:to="loc_us-gaap_SegmentDomain_019ce7a5-4819-7eb5-9809-81bcd90b80da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4819-738d-9ffa-2cfb85688622" xlink:href="jrvr-20260331.xsd#jrvr_ExcessAndSurplusLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4819-7eb5-9809-81bcd90b80da" xlink:to="loc_jrvr_ExcessAndSurplusLinesMember_019ce7a5-4819-738d-9ffa-2cfb85688622" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_SpecialtyAdmittedInsuranceMember_019ce7a5-4819-7b0f-9611-de151bcc31d6" xlink:href="jrvr-20260331.xsd#jrvr_SpecialtyAdmittedInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ce7a5-4819-7eb5-9809-81bcd90b80da" xlink:to="loc_jrvr_SpecialtyAdmittedInsuranceMember_019ce7a5-4819-7b0f-9611-de151bcc31d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4819-7f67-b089-9cbb227b1eaf" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ce7a5-4819-7f82-8425-c00393368fe9" xlink:to="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4819-7f67-b089-9cbb227b1eaf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4819-7f67-b089-9cbb227b1eaf_default" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4819-7f67-b089-9cbb227b1eaf" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4819-7f67-b089-9cbb227b1eaf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4819-72bc-b34b-889d9efb5dd0" xlink:href="jrvr-20260331.xsd#jrvr_ReinsuranceTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_jrvr_ReinsuranceTransactionAxis_019ce7a5-4819-7f67-b089-9cbb227b1eaf" xlink:to="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4819-72bc-b34b-889d9efb5dd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialAutoLPTAndESADCMember_019ce7a5-4819-72eb-8e2e-fba19012b2ad" xlink:href="jrvr-20260331.xsd#jrvr_CommercialAutoLPTAndESADCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_jrvr_ReinsuranceTransactionDomain_019ce7a5-4819-72bc-b34b-889d9efb5dd0" xlink:to="loc_jrvr_CommercialAutoLPTAndESADCMember_019ce7a5-4819-72eb-8e2e-fba19012b2ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_UnderwritingProfitLossOfOperatingSegments_019ce7a5-4819-754b-9865-88502ba95de0" xlink:href="jrvr-20260331.xsd#jrvr_UnderwritingProfitLossOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_jrvr_UnderwritingProfitLossOfOperatingSegments_019ce7a5-4819-754b-9865-88502ba95de0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_OtherOperatingExpensesOfCorporateAndOtherSegment_019ce7a5-4819-759b-a13a-0913dfdd0c6f" xlink:href="jrvr-20260331.xsd#jrvr_OtherOperatingExpensesOfCorporateAndOtherSegment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_jrvr_OtherOperatingExpensesOfCorporateAndOtherSegment_019ce7a5-4819-759b-a13a-0913dfdd0c6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_UnderwritingProfitLoss_019ce7a5-4819-7023-b833-8b7260870db1" xlink:href="jrvr-20260331.xsd#jrvr_UnderwritingProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_jrvr_UnderwritingProfitLoss_019ce7a5-4819-7023-b833-8b7260870db1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ce7a5-4819-7997-aad5-c4e8fb60a9c6" xlink:href="jrvr-20260331.xsd#jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_jrvr_PriorYearClaimsAndClaimsAdjustmentExpenseRetroactiveReinsurance_019ce7a5-4819-7997-aad5-c4e8fb60a9c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019ce7a5-4819-7786-9005-fbba99c0fe9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_us-gaap_NetInvestmentIncome_019ce7a5-4819-7786-9005-fbba99c0fe9e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019ce7a5-4819-7b78-ad0e-1cd36ab3617c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_us-gaap_GainLossOnInvestments_019ce7a5-4819-7b78-ad0e-1cd36ab3617c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_OtherIncomeAndExpenses_019ce7a5-4819-7113-98f7-96bb4012e7a6" xlink:href="jrvr-20260331.xsd#jrvr_OtherIncomeAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_jrvr_OtherIncomeAndExpenses_019ce7a5-4819-7113-98f7-96bb4012e7a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_019ce7a5-4819-7be2-8ab9-888ea6cd7f2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_us-gaap_InterestExpense_019ce7a5-4819-7be2-8ab9-888ea6cd7f2b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019ce7a5-4819-73a0-97f5-1b0b6577872e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019ce7a5-4819-73a0-97f5-1b0b6577872e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019ce7a5-4819-77c0-b5da-acdad21bd532" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ce7a5-4819-7517-996d-d61892f0a8e5" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019ce7a5-4819-77c0-b5da-acdad21bd532" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SeniorDebtDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019ce7a5-4819-7942-8583-1f940ea7f000" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:to="loc_us-gaap_DebtInstrumentTable_019ce7a5-4819-7942-8583-1f940ea7f000" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019d4273-0fb3-7ff9-af23-1a21915de48c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ce7a5-4819-7942-8583-1f940ea7f000" xlink:to="loc_us-gaap_CreditFacilityAxis_019d4273-0fb3-7ff9-af23-1a21915de48c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d4273-0fb3-7ff9-af23-1a21915de48c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019d4273-0fb3-7ff9-af23-1a21915de48c" xlink:to="loc_us-gaap_CreditFacilityDomain_019d4273-0fb3-7ff9-af23-1a21915de48c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d4273-0fb3-73bd-a761-a5f22894a81e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019d4273-0fb3-7ff9-af23-1a21915de48c" xlink:to="loc_us-gaap_CreditFacilityDomain_019d4273-0fb3-73bd-a761-a5f22894a81e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_A2013FacilityMember_019d4273-0fb3-7b10-8de0-241b73c9b6e4" xlink:href="jrvr-20260331.xsd#jrvr_A2013FacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d4273-0fb3-73bd-a761-a5f22894a81e" xlink:to="loc_jrvr_A2013FacilityMember_019d4273-0fb3-7b10-8de0-241b73c9b6e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CreditAgreementMember_019d4273-0fb3-74a9-b488-d0d571ae10fe" xlink:href="jrvr-20260331.xsd#jrvr_CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d4273-0fb3-73bd-a761-a5f22894a81e" xlink:to="loc_jrvr_CreditAgreementMember_019d4273-0fb3-74a9-b488-d0d571ae10fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019d4273-0fb3-74c6-ae38-15759796f6c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019ce7a5-4819-7942-8583-1f940ea7f000" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019d4273-0fb3-74c6-ae38-15759796f6c9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019d4273-0fb3-74c6-ae38-15759796f6c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019d4273-0fb3-74c6-ae38-15759796f6c9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019d4273-0fb3-74c6-ae38-15759796f6c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019d4273-0fb3-7ed1-b79c-b98f11e927ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019d4273-0fb3-74c6-ae38-15759796f6c9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019d4273-0fb3-7ed1-b79c-b98f11e927ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019d4273-0fb3-7e18-b38f-a091235d13a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019d4273-0fb3-7ed1-b79c-b98f11e927ff" xlink:to="loc_us-gaap_UnsecuredDebtMember_019d4273-0fb3-7e18-b38f-a091235d13a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019d4273-0fb3-712d-ad67-7649435677c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019d4273-0fb3-7ed1-b79c-b98f11e927ff" xlink:to="loc_us-gaap_SecuredDebtMember_019d4273-0fb3-712d-ad67-7649435677c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d4273-0fb3-7a4e-861b-49f61487d9fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d4273-0fb3-7a4e-861b-49f61487d9fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_019d4273-0fb3-7d5b-8ccb-4be594e7b0e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_019d4273-0fb3-7d5b-8ccb-4be594e7b0e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019d4273-0fb3-7b19-8ae9-214f9ccc212d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtPercentageBearingVariableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019d4273-0fb3-7b19-8ae9-214f9ccc212d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019d4273-0fb3-7185-8f37-e1eb96bdf6d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019d4273-0fb3-7185-8f37-e1eb96bdf6d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019d4273-0fb3-7255-bf55-ab63ea2c0bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:to="loc_us-gaap_LineOfCredit_019d4273-0fb3-7255-bf55-ab63ea2c0bf1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019d4273-0fb3-7399-b56f-6d4f82996157" xlink:href="jrvr-20260331.xsd#jrvr_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019ce7a5-4819-7558-96c3-23e006b62b7c" xlink:to="loc_jrvr_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019d4273-0fb3-7399-b56f-6d4f82996157" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/FairValueMeasurementsScheduleofAssetsFairValueonaRecurringBasisDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-7665-9190-25a447c59b3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7a8d-9fdf-b1d8742ca20a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-7665-9190-25a447c59b3c" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7a8d-9fdf-b1d8742ca20a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-7d9c-9d9b-c174091ec4d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7a8d-9fdf-b1d8742ca20a" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-7d9c-9d9b-c174091ec4d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-7d9c-9d9b-c174091ec4d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-7d9c-9d9b-c174091ec4d1" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-7d9c-9d9b-c174091ec4d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-75f5-9a6a-4cd7faa6ab9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-7d9c-9d9b-c174091ec4d1" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-75f5-9a6a-4cd7faa6ab9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019ce7a5-4819-7b3a-8fa0-97b7576b919e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-75f5-9a6a-4cd7faa6ab9d" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019ce7a5-4819-7b3a-8fa0-97b7576b919e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce7a5-4819-72c7-af94-0b97e730333e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7a8d-9fdf-b1d8742ca20a" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce7a5-4819-72c7-af94-0b97e730333e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce7a5-4819-72c7-af94-0b97e730333e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce7a5-4819-72c7-af94-0b97e730333e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce7a5-4819-72c7-af94-0b97e730333e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce7a5-4819-7d89-8cef-8bba47d47761" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ce7a5-4819-72c7-af94-0b97e730333e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce7a5-4819-7d89-8cef-8bba47d47761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019ce7a5-4819-74f3-a1d0-8528dad41e96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce7a5-4819-7d89-8cef-8bba47d47761" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019ce7a5-4819-74f3-a1d0-8528dad41e96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019ce7a5-4819-778d-97e7-c6cdeeae4d01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce7a5-4819-7d89-8cef-8bba47d47761" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019ce7a5-4819-778d-97e7-c6cdeeae4d01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019ce7a5-4819-7f90-b657-514cb7dabfbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ce7a5-4819-7d89-8cef-8bba47d47761" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019ce7a5-4819-7f90-b657-514cb7dabfbb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4819-771c-a591-217bd77f1eb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7a8d-9fdf-b1d8742ca20a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4819-771c-a591-217bd77f1eb4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4819-771c-a591-217bd77f1eb4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4819-771c-a591-217bd77f1eb4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4819-771c-a591-217bd77f1eb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4819-7549-ac7f-f1a5c4a1e745" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019ce7a5-4819-771c-a591-217bd77f1eb4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4819-7549-ac7f-f1a5c4a1e745" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4819-768b-974a-ae789652815f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4819-7549-ac7f-f1a5c4a1e745" xlink:to="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4819-768b-974a-ae789652815f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019ce7a5-4819-76e5-896a-dddf1fc7495d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4819-768b-974a-ae789652815f" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019ce7a5-4819-76e5-896a-dddf1fc7495d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019ce7a5-4819-76cd-ad50-95fc75c55201" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4819-768b-974a-ae789652815f" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019ce7a5-4819-76cd-ad50-95fc75c55201" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019ce7a5-4819-7960-8cf9-c6c42b7f2ad8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4819-768b-974a-ae789652815f" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019ce7a5-4819-7960-8cf9-c6c42b7f2ad8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_019ce7a5-4819-7350-9075-73e7ecc15f2e" xlink:href="jrvr-20260331.xsd#jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4819-768b-974a-ae789652815f" xlink:to="loc_jrvr_CommercialMortgageBackedAndAssetBackedSecuritiesMember_019ce7a5-4819-7350-9075-73e7ecc15f2e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019ce7a5-4819-7e30-b274-9d540b469269" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesMember_019ce7a5-4819-768b-974a-ae789652815f" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019ce7a5-4819-7e30-b274-9d540b469269" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019ce7a5-4819-759f-981f-6639e47f9f94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019ce7a5-4819-7549-ac7f-f1a5c4a1e745" xlink:to="loc_us-gaap_EquitySecuritiesMember_019ce7a5-4819-759f-981f-6639e47f9f94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_019ce7a5-4819-7e3c-bfb9-f45073849895" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesMember_019ce7a5-4819-759f-981f-6639e47f9f94" xlink:to="loc_us-gaap_PreferredStockMember_019ce7a5-4819-7e3c-bfb9-f45073849895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ce7a5-4819-7e84-9b7a-fc5c1d34b3b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesMember_019ce7a5-4819-759f-981f-6639e47f9f94" xlink:to="loc_us-gaap_CommonStockMember_019ce7a5-4819-7e84-9b7a-fc5c1d34b3b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAbstract_019ce7a5-4819-7039-9764-8b6580add855" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-7665-9190-25a447c59b3c" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAbstract_019ce7a5-4819-7039-9764-8b6580add855" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce7a5-4819-71df-a11f-ece68c9dfda3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_019ce7a5-4819-7039-9764-8b6580add855" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce7a5-4819-71df-a11f-ece68c9dfda3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsAbstract_019ce7a5-4819-7640-b1ea-d89bc65185bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermInvestmentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-7665-9190-25a447c59b3c" xlink:to="loc_us-gaap_ShortTermInvestmentsAbstract_019ce7a5-4819-7640-b1ea-d89bc65185bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019ce7a5-4819-7c43-a399-e2536c33e486" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermInvestmentsAbstract_019ce7a5-4819-7640-b1ea-d89bc65185bd" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019ce7a5-4819-7c43-a399-e2536c33e486" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_019ce7a5-4819-7a45-bb69-0acad5438f38" xlink:href="jrvr-20260331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-7665-9190-25a447c59b3c" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_019ce7a5-4819-7a45-bb69-0acad5438f38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherShortTermInvestments_019ce7a5-4819-7164-bc61-5400d9d76951" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-7665-9190-25a447c59b3c" xlink:to="loc_us-gaap_OtherShortTermInvestments_019ce7a5-4819-7164-bc61-5400d9d76951" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/FairValueMeasurementsScheduleofAvailableforSaleFixedMaturitySecuritiesMeasuredatFairValueonaRecurringBasisDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-7c74-9f6f-bead20b81a51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019ce7a5-4819-7805-82ed-6a15ca58b213" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019ce7a5-4819-7c74-9f6f-bead20b81a51" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019ce7a5-4819-7805-82ed-6a15ca58b213" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-75fe-8963-d70dd903c84b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019ce7a5-4819-7805-82ed-6a15ca58b213" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-75fe-8963-d70dd903c84b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-75fe-8963-d70dd903c84b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-75fe-8963-d70dd903c84b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-75fe-8963-d70dd903c84b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-76bf-9711-75765206de82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ce7a5-4819-75fe-8963-d70dd903c84b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-76bf-9711-75765206de82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019ce7a5-4819-768e-b38b-7d8c38d4c24a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ce7a5-4819-76bf-9711-75765206de82" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019ce7a5-4819-768e-b38b-7d8c38d4c24a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019ce7a5-4819-7b79-a7ee-fa9374c08baf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019ce7a5-4819-7805-82ed-6a15ca58b213" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019ce7a5-4819-7b79-a7ee-fa9374c08baf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019ce7a5-4819-7b79-a7ee-fa9374c08baf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019ce7a5-4819-7b79-a7ee-fa9374c08baf" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019ce7a5-4819-7b79-a7ee-fa9374c08baf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019ce7a5-4819-7deb-9e12-84162aa09661" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019ce7a5-4819-7b79-a7ee-fa9374c08baf" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019ce7a5-4819-7deb-9e12-84162aa09661" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesAssetsMember_019ce7a5-4819-7917-86c6-c7b39d575d43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuritiesAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019ce7a5-4819-7deb-9e12-84162aa09661" xlink:to="loc_us-gaap_SecuritiesAssetsMember_019ce7a5-4819-7917-86c6-c7b39d575d43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019ce7a5-4819-7c74-9f6f-bead20b81a51" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019ce7a5-4819-7375-a7d5-fb23b154f2d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019ce7a5-4819-7375-a7d5-fb23b154f2d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_019ce7a5-4819-7558-b2f8-3117532b8f59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_019ce7a5-4819-7558-b2f8-3117532b8f59" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_019ce7a5-4819-778f-a8a1-febc55130e16" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_019ce7a5-4819-778f-a8a1-febc55130e16" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019ce7a5-4819-757f-b0e0-7b274da94ef3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019ce7a5-4819-757f-b0e0-7b274da94ef3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_019ce7a5-4819-796a-8c94-658cd713e479" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_019ce7a5-4819-796a-8c94-658cd713e479" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_019ce7a5-4819-7eb5-965a-c1553e6d14ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_019ce7a5-4819-7eb5-965a-c1553e6d14ac" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetAmortizationofDiscount_019ce7a5-4819-7d6b-9e20-59d6e313c1e5" xlink:href="jrvr-20260331.xsd#jrvr_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetAmortizationofDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_jrvr_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetAmortizationofDiscount_019ce7a5-4819-7d6b-9e20-59d6e313c1e5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019ce7a5-4819-7066-ad37-063b88b7b705" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019ce7a5-4819-7066-ad37-063b88b7b705" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_019ce7a5-4819-711b-b8f6-d657dd7198d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019ce7a5-4819-723f-947b-13d6499beccb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_019ce7a5-4819-711b-b8f6-d657dd7198d7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019ce7a5-4819-73a2-8904-51d033955e57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/FairValueMeasurementsScheduleoftheCarryingValueandFairValuesofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-775f-a0a0-8f307aea32a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7ad7-b21d-3c65de5b9e0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-775f-a0a0-8f307aea32a4" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7ad7-b21d-3c65de5b9e0b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019ce7a5-4819-774d-a274-6fb10e889c42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019ce7a5-4819-7ad7-b21d-3c65de5b9e0b" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019ce7a5-4819-774d-a274-6fb10e889c42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019ce7a5-4819-774d-a274-6fb10e889c42_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019ce7a5-4819-774d-a274-6fb10e889c42" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019ce7a5-4819-774d-a274-6fb10e889c42_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019ce7a5-4819-7101-8e6b-184e521e4d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019ce7a5-4819-774d-a274-6fb10e889c42" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019ce7a5-4819-7101-8e6b-184e521e4d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019ce7a5-4819-73e5-a5d0-f8b689fc0bd2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019ce7a5-4819-7101-8e6b-184e521e4d1d" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019ce7a5-4819-73e5-a5d0-f8b689fc0bd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019ce7a5-4819-783c-a36e-ffbb5b0c86d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019ce7a5-4819-73e5-a5d0-f8b689fc0bd2" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019ce7a5-4819-783c-a36e-ffbb5b0c86d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019ce7a5-4819-7410-b18e-23759daad8f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019ce7a5-4819-73e5-a5d0-f8b689fc0bd2" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019ce7a5-4819-7410-b18e-23759daad8f6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-775f-a0a0-8f307aea32a4" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce7a5-4819-7128-883c-1302f4c47197" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019ce7a5-4819-7128-883c-1302f4c47197" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019ce7a5-4819-79fd-819b-f966fe503400" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_019ce7a5-4819-79fd-819b-f966fe503400" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_019ce7a5-4819-7b9f-b5a9-e9c312e5adaa" xlink:href="jrvr-20260331.xsd#jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:to="loc_jrvr_FairValueOptionLoansHeldasAssetsAggregateFairValue_019ce7a5-4819-7b9f-b5a9-e9c312e5adaa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ce7a5-4819-782b-aba4-0eb9931b522f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ce7a5-4819-782b-aba4-0eb9931b522f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashEquivalents_019ce7a5-4819-7666-b033-d8fe7538a705" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:to="loc_us-gaap_RestrictedCashEquivalents_019ce7a5-4819-7666-b033-d8fe7538a705" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherShortTermInvestments_019ce7a5-4819-7aba-bbaf-fecec0aa43ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:to="loc_us-gaap_OtherShortTermInvestments_019ce7a5-4819-7aba-bbaf-fecec0aa43ad" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NotesReceivable_019ce7a5-4819-7592-879c-ead3f316295f" xlink:href="jrvr-20260331.xsd#jrvr_NotesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019ce7a5-4819-7c10-8179-e380346d6c23" xlink:to="loc_jrvr_NotesReceivable_019ce7a5-4819-7592-879c-ead3f316295f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019ce7a5-4819-7df4-b620-00b8af43b8c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019ce7a5-4819-775f-a0a0-8f307aea32a4" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019ce7a5-4819-7df4-b620-00b8af43b8c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019ce7a5-4819-7125-a24f-9a657d0ce040" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019ce7a5-4819-7df4-b620-00b8af43b8c2" xlink:to="loc_us-gaap_LineOfCredit_019ce7a5-4819-7125-a24f-9a657d0ce040" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_019ce7a5-4819-7056-9851-d5d4ad6e16f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019ce7a5-4819-7df4-b620-00b8af43b8c2" xlink:to="loc_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_019ce7a5-4819-7056-9851-d5d4ad6e16f2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SeriesAPreferredSharesDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_019ce7a5-4819-7100-86bc-ee67e877187f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_019ce7a5-4819-7100-86bc-ee67e877187f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019d4206-54ae-77cd-8d1b-62a4888c3853" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_019ce7a5-4819-7100-86bc-ee67e877187f" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019d4206-54ae-77cd-8d1b-62a4888c3853" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019d4206-54ae-77cd-8d1b-62a4888c3853_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019d4206-54ae-77cd-8d1b-62a4888c3853" xlink:to="loc_us-gaap_ClassOfStockDomain_019d4206-54ae-77cd-8d1b-62a4888c3853_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019d4206-54ae-70a0-b73b-f92a0f5edf16" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019d4206-54ae-77cd-8d1b-62a4888c3853" xlink:to="loc_us-gaap_ClassOfStockDomain_019d4206-54ae-70a0-b73b-f92a0f5edf16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_019d4206-54ae-79ba-bc88-e021c87e6b75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019d4206-54ae-70a0-b73b-f92a0f5edf16" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_019d4206-54ae-79ba-bc88-e021c87e6b75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019d4206-54ae-7a64-b985-2b1504f07309" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_019ce7a5-4819-7100-86bc-ee67e877187f" xlink:to="loc_srt_StatementScenarioAxis_019d4206-54ae-7a64-b985-2b1504f07309" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019d4206-54ae-7a64-b985-2b1504f07309_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019d4206-54ae-7a64-b985-2b1504f07309" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019d4206-54ae-7a64-b985-2b1504f07309_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019d4206-54ae-7127-9eac-12df2efdfcb9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019d4206-54ae-7a64-b985-2b1504f07309" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019d4206-54ae-7127-9eac-12df2efdfcb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019d4206-54ae-7fe6-a002-a4b0308ba99c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019d4206-54ae-7127-9eac-12df2efdfcb9" xlink:to="loc_srt_ScenarioForecastMember_019d4206-54ae-7fe6-a002-a4b0308ba99c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019d4206-54ae-7a2a-97e1-1b3f1cb9f17c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_019ce7a5-4819-7100-86bc-ee67e877187f" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019d4206-54ae-7a2a-97e1-1b3f1cb9f17c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d4206-54ae-7a2a-97e1-1b3f1cb9f17c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d4206-54ae-7a2a-97e1-1b3f1cb9f17c" xlink:to="loc_us-gaap_EquityComponentDomain_019d4206-54ae-7a2a-97e1-1b3f1cb9f17c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019d4206-54ae-7078-a887-5a048ec84e2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019d4206-54ae-7a2a-97e1-1b3f1cb9f17c" xlink:to="loc_us-gaap_EquityComponentDomain_019d4206-54ae-7078-a887-5a048ec84e2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019d4206-54ae-7ab0-898a-ea7145b7536e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019d4206-54ae-7078-a887-5a048ec84e2e" xlink:to="loc_us-gaap_CommonStockMember_019d4206-54ae-7ab0-898a-ea7145b7536e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingAMBestAxis_019d4206-7d41-7301-8f53-65224c3155e6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CreditRatingAMBestAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_019ce7a5-4819-7100-86bc-ee67e877187f" xlink:to="loc_srt_CreditRatingAMBestAxis_019d4206-7d41-7301-8f53-65224c3155e6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingAMBestDomain_019d4206-7d41-7301-8f53-65224c3155e6_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CreditRatingAMBestDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CreditRatingAMBestAxis_019d4206-7d41-7301-8f53-65224c3155e6" xlink:to="loc_srt_CreditRatingAMBestDomain_019d4206-7d41-7301-8f53-65224c3155e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CreditRatingAMBestDomain_019d4206-7d41-7bf0-aee8-c15a4c991ec6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CreditRatingAMBestDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CreditRatingAMBestAxis_019d4206-7d41-7301-8f53-65224c3155e6" xlink:to="loc_srt_CreditRatingAMBestDomain_019d4206-7d41-7bf0-aee8-c15a4c991ec6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_AMBestBelowARatingMember_019d4206-7d41-7219-982a-fe96e7f1229f" xlink:href="jrvr-20260331.xsd#jrvr_AMBestBelowARatingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CreditRatingAMBestDomain_019d4206-7d41-7bf0-aee8-c15a4c991ec6" xlink:to="loc_jrvr_AMBestBelowARatingMember_019d4206-7d41-7219-982a-fe96e7f1229f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_019d4206-54ae-75c6-a279-390fa140f048" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_019d4206-54ae-75c6-a279-390fa140f048" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendRatePercentage_019d4206-54ae-70e4-8e38-14befb8ccc0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockDividendRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_PreferredStockDividendRatePercentage_019d4206-54ae-70e4-8e38-14befb8ccc0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_019d4206-54ae-7efb-98cf-c1a8485885f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_019d4206-54ae-7efb-98cf-c1a8485885f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_019d4206-54ae-7336-82b1-433a169a4501" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TemporaryEquityLiquidationPreferencePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_019d4206-54ae-7336-82b1-433a169a4501" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDividendTerm_019d4206-54ae-7c0b-89bd-aa7ad507c9d1" xlink:href="jrvr-20260331.xsd#jrvr_PreferredStockDividendTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_PreferredStockDividendTerm_019d4206-54ae-7c0b-89bd-aa7ad507c9d1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDividendPaymentRateVariableSpread_019d4206-54ae-7931-b0bb-72b96d93396f" xlink:href="jrvr-20260331.xsd#jrvr_PreferredStockDividendPaymentRateVariableSpread"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_PreferredStockDividendPaymentRateVariableSpread_019d4206-54ae-7931-b0bb-72b96d93396f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_019d4206-54ae-775d-9246-1cbe143ac53a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_DividendsPreferredStock_019d4206-54ae-775d-9246-1cbe143ac53a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionPrice_019d4206-54ae-712f-96e0-9694b1840350" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockConvertibleConversionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionPrice_019d4206-54ae-712f-96e0-9694b1840350" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_019d4206-54ae-7601-8052-485ab7855d37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_019d4206-54ae-7601-8052-485ab7855d37" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommonStockCovenantThresholdPerShare_019d4206-54ae-7eb1-9579-c7a17061d3cb" xlink:href="jrvr-20260331.xsd#jrvr_CommonStockCovenantThresholdPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_CommonStockCovenantThresholdPerShare_019d4206-54ae-7eb1-9579-c7a17061d3cb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_CommonStockDividendPerShareCashPaymentsThreshold_019d4206-54ae-7bba-860e-ed0f4a2f7a71" xlink:href="jrvr-20260331.xsd#jrvr_CommonStockDividendPerShareCashPaymentsThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_CommonStockDividendPerShareCashPaymentsThreshold_019d4206-54ae-7bba-860e-ed0f4a2f7a71" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleMandatoryConversionPercentage_019d4206-54ae-72fe-8ea5-6776a712d935" xlink:href="jrvr-20260331.xsd#jrvr_PreferredStockConvertibleMandatoryConversionPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_PreferredStockConvertibleMandatoryConversionPercentage_019d4206-54ae-72fe-8ea5-6776a712d935" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleNumberOfTradingDays_019d4206-54ae-7461-903b-89c7adc5f3cf" xlink:href="jrvr-20260331.xsd#jrvr_PreferredStockConvertibleNumberOfTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_PreferredStockConvertibleNumberOfTradingDays_019d4206-54ae-7461-903b-89c7adc5f3cf" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDiscountRatePercentage_019d4206-54ae-7464-8af7-43e414321fd2" xlink:href="jrvr-20260331.xsd#jrvr_PreferredStockDiscountRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_PreferredStockDiscountRatePercentage_019d4206-54ae-7464-8af7-43e414321fd2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockDividendTradingDays_019d4206-54ae-72a1-b292-e049ec62e283" xlink:href="jrvr-20260331.xsd#jrvr_PreferredStockDividendTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_PreferredStockDividendTradingDays_019d4206-54ae-72a1-b292-e049ec62e283" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_019d4206-54ae-7e8c-a9d2-f7818be056c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_us-gaap_PreferredStockValue_019d4206-54ae-7e8c-a9d2-f7818be056c7" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PreferredStockConvertibleVotingEquityMaximum_019d4206-7d41-7271-8532-4546d03a7f00" xlink:href="jrvr-20260331.xsd#jrvr_PreferredStockConvertibleVotingEquityMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_019ce7a5-4819-7502-b566-f93f3cb26eb8" xlink:to="loc_jrvr_PreferredStockConvertibleVotingEquityMaximum_019d4206-7d41-7271-8532-4546d03a7f00" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsCommonSharesDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-74b5-9890-02c670f2f70e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-790c-9f84-1ac35e77bb69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-74b5-9890-02c670f2f70e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-790c-9f84-1ac35e77bb69" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4819-77f9-9a32-1d28feb78e45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-790c-9f84-1ac35e77bb69" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4819-77f9-9a32-1d28feb78e45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ce7a5-4819-77f9-9a32-1d28feb78e45_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4819-77f9-9a32-1d28feb78e45" xlink:to="loc_us-gaap_EquityComponentDomain_019ce7a5-4819-77f9-9a32-1d28feb78e45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ce7a5-4819-7377-a0a9-46916cd2f0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ce7a5-4819-77f9-9a32-1d28feb78e45" xlink:to="loc_us-gaap_EquityComponentDomain_019ce7a5-4819-7377-a0a9-46916cd2f0cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ce7a5-4819-72ce-988e-f021f0048859" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ce7a5-4819-7377-a0a9-46916cd2f0cc" xlink:to="loc_us-gaap_CommonStockMember_019ce7a5-4819-72ce-988e-f021f0048859" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7cac-8273-6e79852f6cb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-790c-9f84-1ac35e77bb69" xlink:to="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7cac-8273-6e79852f6cb4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7cac-8273-6e79852f6cb4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7cac-8273-6e79852f6cb4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7cac-8273-6e79852f6cb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7606-abc8-2d3dccea8d18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7cac-8273-6e79852f6cb4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7606-abc8-2d3dccea8d18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce7a5-4819-7c45-aef6-3a40d3395085" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7606-abc8-2d3dccea8d18" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce7a5-4819-7c45-aef6-3a40d3395085" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ce7a5-4819-7cc9-8899-7cff5b6e7546" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-74b5-9890-02c670f2f70e" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ce7a5-4819-7cc9-8899-7cff5b6e7546" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019ce7a5-4819-725d-9f4b-292437c09507" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-74b5-9890-02c670f2f70e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019ce7a5-4819-725d-9f4b-292437c09507" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_RestrictedStockUnitDividendEquivalents_019ce7a5-4819-7119-b3a6-45c81d916f32" xlink:href="jrvr-20260331.xsd#jrvr_RestrictedStockUnitDividendEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-74b5-9890-02c670f2f70e" xlink:to="loc_jrvr_RestrictedStockUnitDividendEquivalents_019ce7a5-4819-7119-b3a6-45c81d916f32" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_019ce7a5-4819-7ce0-aa2e-d91664715663" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-74b5-9890-02c670f2f70e" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_019ce7a5-4819-7ce0-aa2e-d91664715663" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsEquityIncentivePlansDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-76b5-af18-2f85b9935d94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-76b5-af18-2f85b9935d94" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019d41ca-9fa7-72eb-b56f-ab250552c928" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-76b5-af18-2f85b9935d94" xlink:to="loc_us-gaap_PlanNameAxis_019d41ca-9fa7-72eb-b56f-ab250552c928" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019d41ca-9fa7-72eb-b56f-ab250552c928_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019d41ca-9fa7-72eb-b56f-ab250552c928" xlink:to="loc_us-gaap_PlanNameDomain_019d41ca-9fa7-72eb-b56f-ab250552c928_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019d41ca-9fa7-76ec-afd7-56f2361d6310" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019d41ca-9fa7-72eb-b56f-ab250552c928" xlink:to="loc_us-gaap_PlanNameDomain_019d41ca-9fa7-76ec-afd7-56f2361d6310" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_LongTermIncentivePlan2014Member_019d41ca-9fa7-7a2e-b7cc-215bdd4ffd91" xlink:href="jrvr-20260331.xsd#jrvr_LongTermIncentivePlan2014Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019d41ca-9fa7-76ec-afd7-56f2361d6310" xlink:to="loc_jrvr_LongTermIncentivePlan2014Member_019d41ca-9fa7-7a2e-b7cc-215bdd4ffd91" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NonEmployeeDirectorIncentivePlan2014Member_019d41ca-d7d5-7559-8197-d1cf1d5bdec0" xlink:href="jrvr-20260331.xsd#jrvr_NonEmployeeDirectorIncentivePlan2014Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019d41ca-9fa7-76ec-afd7-56f2361d6310" xlink:to="loc_jrvr_NonEmployeeDirectorIncentivePlan2014Member_019d41ca-d7d5-7559-8197-d1cf1d5bdec0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019d41ca-9fa7-7e66-8924-5e6c78b3798f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-76b5-af18-2f85b9935d94" xlink:to="loc_us-gaap_AwardTypeAxis_019d41ca-9fa7-7e66-8924-5e6c78b3798f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d41ca-9fa7-7e66-8924-5e6c78b3798f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019d41ca-9fa7-7e66-8924-5e6c78b3798f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d41ca-9fa7-7e66-8924-5e6c78b3798f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d41ca-9fa7-7cc2-af9f-30f5743853fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019d41ca-9fa7-7e66-8924-5e6c78b3798f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d41ca-9fa7-7cc2-af9f-30f5743853fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PRSUMember_019d41ca-9fa7-764d-96e7-4c2b561cff18" xlink:href="jrvr-20260331.xsd#jrvr_PRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d41ca-9fa7-7cc2-af9f-30f5743853fd" xlink:to="loc_jrvr_PRSUMember_019d41ca-9fa7-764d-96e7-4c2b561cff18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019d41ca-9fa7-7be1-b99f-8daa2264cce9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019d41ca-9fa7-7be1-b99f-8daa2264cce9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019d41ca-9fa7-7832-bd5d-a20b5be3d1ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019d41ca-9fa7-7832-bd5d-a20b5be3d1ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019d41ca-9fa7-799b-88e0-4ad817e26b03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019d41ca-9fa7-799b-88e0-4ad817e26b03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardContingentRightNumberOfSharesToBeReceived_019d41ca-9fa7-7121-b81d-bf881c6f904e" xlink:href="jrvr-20260331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardContingentRightNumberOfSharesToBeReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardContingentRightNumberOfSharesToBeReceived_019d41ca-9fa7-7121-b81d-bf881c6f904e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019d41ca-9fa7-7edc-988d-6382a93773f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019d41ca-9fa7-7edc-988d-6382a93773f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementThreshold_019d41ca-9fa7-7b18-bb9e-9554324e0f99" xlink:href="jrvr-20260331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementThreshold_019d41ca-9fa7-7b18-bb9e-9554324e0f99" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_019d41ca-9fa7-7dab-9b3a-254f55689547" xlink:href="jrvr-20260331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_019d41ca-9fa7-7dab-9b3a-254f55689547" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementMaximum_019d41ca-9fa7-74c4-83f1-ebae2e6a6980" xlink:href="jrvr-20260331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-77cd-b7b3-cc6f26c0dc3b" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementMaximum_019d41ca-9fa7-74c4-83f1-ebae2e6a6980" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsScheduleofRSUActivityDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-7712-ac84-f898c1c840a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-706f-94c7-659993523b53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-7712-ac84-f898c1c840a0" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-706f-94c7-659993523b53" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-73e9-99ca-74f4c2bbd97e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-706f-94c7-659993523b53" xlink:to="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-73e9-99ca-74f4c2bbd97e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-73e9-99ca-74f4c2bbd97e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-73e9-99ca-74f4c2bbd97e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-73e9-99ca-74f4c2bbd97e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7a87-9fba-e4fdc82a474f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-73e9-99ca-74f4c2bbd97e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7a87-9fba-e4fdc82a474f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce7a5-4819-74b9-84a6-75b6003aaf6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7a87-9fba-e4fdc82a474f" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce7a5-4819-74b9-84a6-75b6003aaf6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_PRSUMember_019ce7a5-4819-76f3-a07a-ca533c12f91f" xlink:href="jrvr-20260331.xsd#jrvr_PRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7a87-9fba-e4fdc82a474f" xlink:to="loc_jrvr_PRSUMember_019ce7a5-4819-76f3-a07a-ca533c12f91f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019ce7a5-4819-774f-88ba-d175352f03ef" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-706f-94c7-659993523b53" xlink:to="loc_srt_TitleOfIndividualAxis_019ce7a5-4819-774f-88ba-d175352f03ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce7a5-4819-774f-88ba-d175352f03ef_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019ce7a5-4819-774f-88ba-d175352f03ef" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce7a5-4819-774f-88ba-d175352f03ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce7a5-4819-7a06-84f2-c845fa61b4b7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019ce7a5-4819-774f-88ba-d175352f03ef" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce7a5-4819-7a06-84f2-c845fa61b4b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_NonemployeeDirectorsMember_019ce7a5-4819-76f0-a966-54413976480e" xlink:href="jrvr-20260331.xsd#jrvr_NonemployeeDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ce7a5-4819-7a06-84f2-c845fa61b4b7" xlink:to="loc_jrvr_NonemployeeDirectorsMember_019ce7a5-4819-76f0-a966-54413976480e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce7a5-4819-706f-b068-03fc32832ea2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-7712-ac84-f898c1c840a0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce7a5-4819-706f-b068-03fc32832ea2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce7a5-4819-7752-a8ba-b9f48080171e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce7a5-4819-706f-b068-03fc32832ea2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce7a5-4819-7752-a8ba-b9f48080171e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ce7a5-4819-7030-a858-0dfc6e995134" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce7a5-4819-706f-b068-03fc32832ea2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ce7a5-4819-7030-a858-0dfc6e995134" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ce7a5-4819-73c4-aa97-b22e5a4fb909" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce7a5-4819-706f-b068-03fc32832ea2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ce7a5-4819-73c4-aa97-b22e5a4fb909" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ce7a5-4819-7a06-8696-8e33101ef5e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce7a5-4819-706f-b068-03fc32832ea2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ce7a5-4819-7a06-8696-8e33101ef5e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustment_019d8a7b-f584-7097-82af-d6d1941f7ccf" xlink:href="jrvr-20260331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ce7a5-4819-706f-b068-03fc32832ea2" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustment_019d8a7b-f584-7097-82af-d6d1941f7ccf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ce7a5-4819-7139-9641-ae60a1b2adb5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce7a5-4819-7b16-a49f-f674bda1e170" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-7712-ac84-f898c1c840a0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce7a5-4819-7b16-a49f-f674bda1e170" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ce7a5-4819-7436-bb7a-b606d2d8042e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce7a5-4819-7b16-a49f-f674bda1e170" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ce7a5-4819-7436-bb7a-b606d2d8042e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ce7a5-4819-7a33-9062-3462eeff982b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce7a5-4819-7b16-a49f-f674bda1e170" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019ce7a5-4819-7a33-9062-3462eeff982b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ce7a5-4819-752c-9a22-3a3117265fda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce7a5-4819-7b16-a49f-f674bda1e170" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ce7a5-4819-752c-9a22-3a3117265fda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ce7a5-4819-7539-b293-1513f2eeba6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce7a5-4819-7b16-a49f-f674bda1e170" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ce7a5-4819-7539-b293-1513f2eeba6d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustmentWeightedAverageGrantDateFairValue_019d8a7c-fba7-770b-b385-4ff6de762480" xlink:href="jrvr-20260331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustmentWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ce7a5-4819-7b16-a49f-f674bda1e170" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustmentWeightedAverageGrantDateFairValue_019d8a7c-fba7-770b-b385-4ff6de762480" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ce7a5-4819-724c-a8bd-cdc8d3b1e3f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019ce7a5-4819-7200-a85f-6bf3935eaa92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-7712-ac84-f898c1c840a0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019ce7a5-4819-7200-a85f-6bf3935eaa92" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_019ce7a5-4819-747d-b1d6-d9db071f2fa4" xlink:href="jrvr-20260331.xsd#jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-7712-ac84-f898c1c840a0" xlink:to="loc_jrvr_ShareBasedCompensationArrangementByShareBasedPaymentAwardPayoutForAchievementTarget_019ce7a5-4819-747d-b1d6-d9db071f2fa4" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/CapitalStockandEquityAwardsCompensationExpenseDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-70c2-b633-53b1e9d6aa8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-7297-8938-0162db875e4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-70c2-b633-53b1e9d6aa8b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-7297-8938-0162db875e4f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7bda-84cc-0ccdfe4106fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ce7a5-4819-7297-8938-0162db875e4f" xlink:to="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7bda-84cc-0ccdfe4106fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7bda-84cc-0ccdfe4106fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7bda-84cc-0ccdfe4106fa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7bda-84cc-0ccdfe4106fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7775-a593-c1a876144f31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ce7a5-4819-7bda-84cc-0ccdfe4106fa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7775-a593-c1a876144f31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce7a5-4819-7add-b67d-3da42c2fd071" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ce7a5-4819-7775-a593-c1a876144f31" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ce7a5-4819-7add-b67d-3da42c2fd071" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019ce7a5-4819-7adf-aff3-8276f7ea86ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-70c2-b633-53b1e9d6aa8b" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019ce7a5-4819-7adf-aff3-8276f7ea86ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ce7a5-4819-7bd0-9007-e65ffaeb0959" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ce7a5-4819-70c2-b633-53b1e9d6aa8b" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ce7a5-4819-7bd0-9007-e65ffaeb0959" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://jrgh.net/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="jrvr-20260331.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_019ce7a5-4819-7e74-ba06-32cc05ef2590" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019ce7a5-4819-7009-8f63-5cf01c634290" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ce7a5-4819-7e74-ba06-32cc05ef2590" xlink:to="loc_us-gaap_SubsequentEventTable_019ce7a5-4819-7009-8f63-5cf01c634290" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019d4191-3a75-7b9e-9866-f81cf7abd6a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ce7a5-4819-7009-8f63-5cf01c634290" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019d4191-3a75-7b9e-9866-f81cf7abd6a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019d4191-3a75-7b9e-9866-f81cf7abd6a7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019d4191-3a75-7b9e-9866-f81cf7abd6a7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019d4191-3a75-7b9e-9866-f81cf7abd6a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019d4191-3a75-7388-9949-92c20cfeb079" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019d4191-3a75-7b9e-9866-f81cf7abd6a7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019d4191-3a75-7388-9949-92c20cfeb079" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019d4191-3a75-7e84-96b9-3b7840391ffb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019d4191-3a75-7388-9949-92c20cfeb079" xlink:to="loc_us-gaap_SubsequentEventMember_019d4191-3a75-7e84-96b9-3b7840391ffb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAxis_019d4191-3a75-7a31-a90d-c881cfc59963" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ce7a5-4819-7009-8f63-5cf01c634290" xlink:to="loc_us-gaap_DividendsAxis_019d4191-3a75-7a31-a90d-c881cfc59963" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_019d4191-3a75-7a31-a90d-c881cfc59963_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DividendsAxis_019d4191-3a75-7a31-a90d-c881cfc59963" xlink:to="loc_us-gaap_DividendsDomain_019d4191-3a75-7a31-a90d-c881cfc59963_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_019d4191-3a75-71a8-9e3a-bfdced8a61b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DividendsAxis_019d4191-3a75-7a31-a90d-c881cfc59963" xlink:to="loc_us-gaap_DividendsDomain_019d4191-3a75-71a8-9e3a-bfdced8a61b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_jrvr_O2026Q2DividendsMember_019d4191-3a75-7d5c-bc2b-102972fc2337" xlink:href="jrvr-20260331.xsd#jrvr_O2026Q2DividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_019d4191-3a75-71a8-9e3a-bfdced8a61b3" xlink:to="loc_jrvr_O2026Q2DividendsMember_019d4191-3a75-7d5c-bc2b-102972fc2337" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019d4191-3a75-7461-84ba-f4d153cf4754" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ce7a5-4819-7009-8f63-5cf01c634290" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019d4191-3a75-7461-84ba-f4d153cf4754" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019d4191-3a75-7461-84ba-f4d153cf4754_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019d4191-3a75-7461-84ba-f4d153cf4754" xlink:to="loc_us-gaap_ClassOfStockDomain_019d4191-3a75-7461-84ba-f4d153cf4754_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019d4191-3a75-7e44-ad69-22b964a9f534" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019d4191-3a75-7461-84ba-f4d153cf4754" xlink:to="loc_us-gaap_ClassOfStockDomain_019d4191-3a75-7e44-ad69-22b964a9f534" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_019d4191-3a75-74c8-b07f-21876a1ca7e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019d4191-3a75-7e44-ad69-22b964a9f534" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_019d4191-3a75-74c8-b07f-21876a1ca7e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_019d4191-3a75-75f8-95af-8754e9e224a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ce7a5-4819-7e74-ba06-32cc05ef2590" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_019d4191-3a75-75f8-95af-8754e9e224a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_019d4191-3a75-77de-9a38-a8f7be2e2a51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendPayableDateToBePaidDayMonthAndYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ce7a5-4819-7e74-ba06-32cc05ef2590" xlink:to="loc_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_019d4191-3a75-77de-9a38-a8f7be2e2a51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_019d4191-3a75-7f36-8db7-5a5547ce3418" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPayableDateOfRecordDayMonthAndYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ce7a5-4819-7e74-ba06-32cc05ef2590" xlink:to="loc_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_019d4191-3a75-7f36-8db7-5a5547ce3418" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_019d4191-3a75-7ce2-8d75-53c452302afb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ce7a5-4819-7e74-ba06-32cc05ef2590" xlink:to="loc_us-gaap_DividendsPreferredStock_019d4191-3a75-7ce2-8d75-53c452302afb" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
