[2] He enrolled in a civil engineering degree course at Dublin Institute of Technology in 1996, but dropped out after 2 years to take on a job in the industry.

[3][6] He later resumed his studies by enrolling in another civil engineering course at Letterkenny Institute of Technology, but dropped out in order to run for Dáil Éireann in the 2002 general election.

He failed to win a seat in the European Parliament, but was elected to Donegal County Council for the Glenties local electoral area.

[9][10] Doherty's second attempt to win a Dáil seat, at the 2007 general election, also proved unsuccessful; he received 21.2% of the first-preference vote.

[10] 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.

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.

[14] Shortly before the 2011 general election, several newspapers alleged that Doherty had misled the public by stating on various Sinn Féin and Oireachtas webpages that he had formerly worked as a "civil engineer", an occupation that presumes a degree-level qualification.

[9][16] Doherty represented Sinn Féin in the Oireachtas delegation that met the Bundestag's Budgetary and European Affairs committees in Berlin in late January 2012.

[21] He topped the poll at the 2020 general election with 21,044 first-preference votes (27.17%),[22] and was appointed leader of Sinn Féin's negotiations team.