On 12 July 2010, the High Court granted Doherty a judicial review into why the government had not held a by-election to fill the Dáil seat vacated by Fianna Fáil's Pat "the Cope" Gallagher when he won election to the European Parliament in June 2009. On 2 November 2010, the High Court ruled that the government had delayed unreasonably in holding the by-election. In response to the ruling, the government announced that the Donegal South-West by-election would be held on 25 November 2010. Doherty stood as the Sinn Féin candidate and won the by-election by a substantial margin, earning 39.8 percent of the first-preference vote. On taking his seat in the Dáil, Doherty was appointed Sinn Féin's spokesperson on Finance. However, the Dáil was dissolved on 1 February 2011, at which point Doherty had been a TD for just over nine weeks.