A by-election was held in the Dáil Éireann Donegal South-West constituency in Ireland on Thursday 25 November 2010, following the election of Fianna Fáil TD Pat "the Cope" Gallagher to the European Parliament at the June 2009 election. Most voters cast their ballots on 25 November 2010; 754 voters on offshore islands (Arranmore, Tory, Inishbofin, Gola, and Inishfree) were entitled to cast their ballots on 22 November. Sinn Féin senator Pearse Doherty was elected on the fourth count.