The Sinn Féin leader has laid a wreath in memory of Irish soldiers who died in the two world wars.
Mary Lou McDonald took part in the remembrance event in Calry Parish Church in Sligo Town.
She laid a laurel wreath in memory of Irish soldiers who died.
Also attending the fourth annual service were Viscount Brookeborough, the Lord Lieutenant for County Fermanagh, and Deike Potzel, the German Ambassador to Ireland.
Mr Potzel laid a wreath on behalf of German soldiers, while Viscount Brookeborough placed a poppy wreath to recall Allied soldiers who died in the two conflicts.
The party's vice-president, Michelle O'Neill, was present on Sunday at a remembrance service to recall the Irish who died in World War One at St Patrick's Cathedral in Dublin.
In 2013 then Sinn Féin Lord Mayor of Belfast, Máirtin Ó Muilleoir, took part in an Armistice Day event for the first time in the party's history.