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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019f8f0c-cb0f-79f0-a4d7-da787d8a2d29,g:42461a68-a938-41e5-856e-2fa0d606d554-->
<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://www.firstmerchants.com/role/DocumentandEntityInformationDocument" xlink:type="simple" xlink:href="frme-20261021.xsd#DocumentandEntityInformationDocument"/>
  <link:definitionLink xlink:role="http://www.firstmerchants.com/role/DocumentandEntityInformationDocument" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityListingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsTable_019f8f0c-cb0f-7b65-9f16-3e7e70a77ea7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityListingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityListingsTable_019f8f0c-cb0f-7b65-9f16-3e7e70a77ea7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f8f0c-cb0f-7264-8737-67c38e77622d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntityListingsTable_019f8f0c-cb0f-7b65-9f16-3e7e70a77ea7" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f8f0c-cb0f-7264-8737-67c38e77622d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f8f0c-cb0f-7264-8737-67c38e77622d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f8f0c-cb0f-7264-8737-67c38e77622d" xlink:to="loc_us-gaap_ClassOfStockDomain_019f8f0c-cb0f-7264-8737-67c38e77622d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f8f0c-cb0f-7f76-975f-56c07cd449ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f8f0c-cb0f-7264-8737-67c38e77622d" xlink:to="loc_us-gaap_ClassOfStockDomain_019f8f0c-cb0f-7f76-975f-56c07cd449ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019f8f0c-cb0f-70e7-936a-16d612adf618" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f8f0c-cb0f-7f76-975f-56c07cd449ad" xlink:to="loc_us-gaap_CommonStockMember_019f8f0c-cb0f-70e7-936a-16d612adf618" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_frme_DepositarySharesMember_019f8f0c-cb0f-7f4c-bed7-df6d79181d78" xlink:href="frme-20261021.xsd#frme_DepositarySharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f8f0c-cb0f-7f76-975f-56c07cd449ad" xlink:to="loc_frme_DepositarySharesMember_019f8f0c-cb0f-7f4c-bed7-df6d79181d78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019f8f0c-cb0f-79d7-b5e8-ee70d0db46f8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_DocumentType_019f8f0c-cb0f-79d7-b5e8-ee70d0db46f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019f8f0c-cb0f-778b-9478-bae125930a01" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_DocumentPeriodEndDate_019f8f0c-cb0f-778b-9478-bae125930a01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019f8f0c-cb0f-76f1-8d7c-edb1469b3853" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityRegistrantName_019f8f0c-cb0f-76f1-8d7c-edb1469b3853" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019f8f0c-cb0f-7812-8204-83aa76159439" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019f8f0c-cb0f-7812-8204-83aa76159439" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019f8f0c-cb0f-742d-a33c-2485cb4d4133" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityFileNumber_019f8f0c-cb0f-742d-a33c-2485cb4d4133" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019f8f0c-cb0f-76ab-bccd-e4be987cc6f9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityTaxIdentificationNumber_019f8f0c-cb0f-76ab-bccd-e4be987cc6f9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019f8f0c-cb0f-7c6a-ab02-db00d8033741" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityAddressAddressLine1_019f8f0c-cb0f-7c6a-ab02-db00d8033741" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019f8f0c-cb0f-7349-8df1-5b67e58999b6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityAddressAddressLine2_019f8f0c-cb0f-7349-8df1-5b67e58999b6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019f8f0c-cb0f-7c33-a838-f3f7dd9de916" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityAddressCityOrTown_019f8f0c-cb0f-7c33-a838-f3f7dd9de916" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019f8f0c-cb0f-7053-8ccd-ecac742c892d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityAddressStateOrProvince_019f8f0c-cb0f-7053-8ccd-ecac742c892d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019f8f0c-cb0f-7f83-bbfb-f14bfa39c7ff" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityAddressPostalZipCode_019f8f0c-cb0f-7f83-bbfb-f14bfa39c7ff" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019f8f0c-cb0f-7fe0-9f22-f107a92c7979" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_CityAreaCode_019f8f0c-cb0f-7fe0-9f22-f107a92c7979" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019f8f0c-cb0f-70e7-a30d-67f927330f9a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_LocalPhoneNumber_019f8f0c-cb0f-70e7-a30d-67f927330f9a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019f8f0c-cb0f-76f5-9a52-a1b2d7741fa0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_Security12bTitle_019f8f0c-cb0f-76f5-9a52-a1b2d7741fa0" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019f8f0c-cb0f-7137-b908-7c18693f82cf" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_TradingSymbol_019f8f0c-cb0f-7137-b908-7c18693f82cf" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019f8f0c-cb0f-728c-951a-335f0e83ae1b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_SecurityExchangeName_019f8f0c-cb0f-728c-951a-335f0e83ae1b" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019f8f0c-cb0f-7164-b3cc-140e0959bf59" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_WrittenCommunications_019f8f0c-cb0f-7164-b3cc-140e0959bf59" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019f8f0c-cb0f-7100-97f5-d0a2e88e7ced" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_SolicitingMaterial_019f8f0c-cb0f-7100-97f5-d0a2e88e7ced" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019f8f0c-cb0f-7296-897e-35df5c95e08e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_PreCommencementTenderOffer_019f8f0c-cb0f-7296-897e-35df5c95e08e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019f8f0c-cb0f-727d-b47d-624426bfa584" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019f8f0c-cb0f-727d-b47d-624426bfa584" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019f8f0c-cb0f-7cc1-9412-393defa790d1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityEmergingGrowthCompany_019f8f0c-cb0f-7cc1-9412-393defa790d1" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019f8f0c-cb0f-7a6c-8d6b-08343fc64cc0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_EntityCentralIndexKey_019f8f0c-cb0f-7a6c-8d6b-08343fc64cc0" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019f8f0c-cb0f-71a1-8406-8f25965839ee" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_019f8f0c-cb0f-7081-95a4-c256be2b4ff0" xlink:to="loc_dei_AmendmentFlag_019f8f0c-cb0f-71a1-8406-8f25965839ee" xlink:type="arc" order="22"/>
  </link:definitionLink>
</link:linkbase>
