In the Garden County final count, Edward Timmons of Fine Gael defeated the departing Fianna Fáil TD. Thirteen years ago, in his maiden run for office, Mr. Donnelly was elected as an Independent in the constituency.

In July 2015, he joined Róisín Shortall and Catherine Murphy in co-founding the Social Democrats.

He had a prominent role in the 2016 election campaign, participating in live television debates on behalf of the Social Democrats. With 14,348 first preferences, or a 20.85% vote share, he would go on to win the most votes in Wicklow that year.

He split from the Social Democrats shortly after the election due to a string of arguments with co-leaders Catherine Murphy and Róisín Shortall.

Mr. Donnelly's preference to start talks about joining the coalition government led by Fine Gael was one of the major points of contention between him and Ms. Shortall and Ms. Murphy, although his co-leaders disapproved of this.

He became a member of Fianna Fáil in February 2017. When the Wicklow constituency was still a five-seater, Mr. Donnelly won the final seat in the 2020 general election.

Wicklow lost four seats when the Wicklow-Wexford constituency was created as a result of boundary changes made in advance of the 2024 general election.