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

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2016-08-17</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001170534</issuerCik>
        <issuerName>MITEL NETWORKS CORP</issuerName>
        <issuerTradingSymbol>MITL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000904495</rptOwnerCik>
            <rptOwnerName>ELLIOTT ASSOCIATES, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>40 WEST 57TH STREET, 30TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common shares, no par value</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4206290</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Notional Principal Amount Derivative Agreements</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2018-01-02</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common shares, no par value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1254712</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This Form 3 is filed by Elliott Associates, L.P. (the &quot;Reporting Person&quot;).</footnote>
        <footnote id="F2">Notional principal amount derivative agreements (the &quot;Derivative Agreements&quot;) in the form of cash settled swaps entered into by the Reporting Person through The Liverpool Limited Partnership, a Bermuda limited partnership and a wholly-owned subsidiary of the Reporting Person (&quot;Liverpool&quot;), at initial execution prices ranging from $6.1362 to $7.2235. The Derivative Agreements provide Liverpool with economic results that are comparable to the economic results of ownership but do not provide it with the power to vote or direct the voting or dispose of or direct the disposition of the shares that are referenced in the Derivative Agreements (such shares, the &quot;Subject Shares&quot;). The Reporting Person disclaims beneficial ownership in the Subject Shares. The counterparties to the Derivative Agreements are unaffiliated third party financial institutions.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Elliott Greenberg, Vice President</signatureName>
        <signatureDate>2016-08-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
