Gethins was appointed a Special Adviser to Scotland's First Minister, Alex Salmond, advising on European and International Affairs as well as Rural Affairs, Energy and Climate Change[3] and subsequently advised Nicola Sturgeon. He was a Political Advisor with the Committee of the Regions in the European Union, a position which saw him working with local authorities from across Europe. He also worked at Scotland Europa.[4]
In February 2015, he was selected by the local party members to contest the 2015 general election at the North East Fife constituency. He won 18,523 votes (a 40.9% share of the vote) and received a majority of 4,344 votes over the Liberal Democrat candidate, Tim Brett, who was selected after the retirement of the seat's long-term Lib Dem MP and former party leader, Sir Ming Campbell.[6][7] In May 2015, the SNP made him their Spokesperson on Europe at Westminster.[8] In July he was appointed as a member of the House of Commons Foreign Affairs Select Committee,[9] the first SNP candidate to win the seat.
At the 2017 general election, Gethins was narrowly re-elected as the MP for North East Fife. He received 13,743 votes, giving him a very slim majority of just two votes over the Liberal Democrats; the joint-third smallest majority in British political history. This was confirmed after three re-counts before being declared.[10] After the election, Gethins was promoted to the SNP Westminster frontbench team of Ian Blackford as the party's Spokesperson for International Affairs and Europe.[11][12]
Despite increasing his share of the vote, he lost his seat at the 2019 general election to the Liberal Democrat candidate, Wendy Chamberlain[13][14] who won by a majority of 1,316 votes.[15] This made him the only SNP MP to lose their seat at the general election that year.
After Westminster
After losing his Westminster seat Gethins was appointed Professor of Practice in International Relations at the University of St Andrews.[16]
In July 2020, Gethins was announced as the chair of ‘eu+me’- a campaign for a close relationship between Scotland and the EU after Brexit.[17]