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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-05-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000899689</issuerCik>
        <issuerName>VORNADO REALTY TRUST</issuerName>
        <issuerTradingSymbol>VNO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001111794</rptOwnerCik>
            <rptOwnerName>TISCH DANIEL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>888 7TH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Units</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-05-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5310</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5310</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5310</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On May 14, 2020, the reporting person received a grant of restricted units (the &quot;Restricted Units&quot;) of Vornado Realty L.P. (the &quot;Operating Partnership&quot;), the operating partnership of Vornado Realty Trust (the &quot;Company&quot;).  The Restricted Units are a class of units of the Operating Partnership that following the occurrence of certain events and upon vesting are convertible by the holder into an equivalent number of Class A Units of the Operating Partnership.  Class A Units are redeemable by the holder for cash or, at the Company's election, Common Shares of the Company on a one for one basis or the cash value of such shares.</footnote>
        <footnote id="F2">These Restricted Units vest immediately.  These units are not transferable until the reporting person is no longer serving as a member of the Company's Board of Trustees, other than in connection with a conversion of the Restricted Units to Class A Units and a redemption of such Class A Units for Common Shares.  Any Common Shares issued in connection with such a redemption must be held by the reporting person until such person is no longer a member of the Company's Board of Trustees.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Steven Santora, Attorney in Fact</signatureName>
        <signatureDate>2020-05-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
