<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-12-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000845877</issuerCik>
        <issuerName>FEDERAL AGRICULTURAL MORTGAGE CORP</issuerName>
        <issuerTradingSymbol>AGM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002102513</rptOwnerCik>
            <rptOwnerName>Pullins Matthew M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O FARMER MAC</rptOwnerStreet1>
            <rptOwnerStreet2>2100 PENNSYLVANIA AVE., NW, SUITE 450N</rptOwnerStreet2>
            <rptOwnerCity>WASHINGTON</rptOwnerCity>
            <rptOwnerState>DC</rptOwnerState>
            <rptOwnerZipCode>20037</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP - CFO and Treasurer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class C Non-Voting Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-12-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1491</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1491</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Grant of time-vested restricted stock units (&quot;RSUs&quot;) under the Amended and Restated 2008 Omnibus Incentive Plan (&quot;Plan&quot;) of the Federal Agricultural Mortgage Corporation (&quot;Farmer Mac&quot;) for no
consideration. Each RSU represents the contingent right to receive, upon vesting, one share of Farmer Mac's Class C Non-Voting Common Stock. Includes three equal installments of 497 RSUs, each of
which will vest on December 11, 2026, December 11, 2027, and December 11, 2028, respectively, if the Reporting Person remains an employee of Farmer Mac on those dates.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Geraldine I. Hayhurst, as attorney-in- fact for Matthew M. Pullins</signatureName>
        <signatureDate>2025-12-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
