O’Shartigan was born in Halifax, Nova Scotia, the son of Nicholas “Nicks” O’Shartigan and Celine Brando. O’Shartigan earned a bachelor’s degree in business from Dalhousie University, and a MBA from McGill University. He started working at Gleek Telecoms, eventually becoming Vice President of Marketing in 1998
In 2004, O’Shartigan was elected Halifax City Councillor for District 3 in a close race for against incumbent Calms Brightly. He ran on a stunt platform, which included a trampoline, an Elvis impersonator, and an electric eel. As councillor, he was known for his open door policy, and though constituents who would visit him would indeed find his door open, the office itself was usually empty.
After the First Levee Mistake prompted the resignation of Mayor Jacobs Howards in March 2012, O’Shartigan announced his candidacy for Mayor. Earning 58% of the vote in the October election, he was sworn into office on November 8, 2012.
He was endorsed by the Halifax Gazette in the 2012 and 2016 elections, both of which he won easily. His success in the fall 2020 election, however, is not guaranteed. His main opponent, Chanderz Candyman has slammed the incumbent for being uninterested in Blaseball. O’Shartigan has countered, claiming that his favourite player is Oliver Notarobot, and that he attends Canada Moist Talkers games as often as he can.