A member of the Liberal Party, MacKinnon is the minister of employment, workforce development and labour, as well as the government house leader.

MacKinnon was born in Charlottetown, Prince Edward Island, and studied business at the Université de Moncton and Queen's University.

From 2007 to 2015, he was Senior Vice-President and National Practice Leader at a global public affairs consultancy firm, where he led teams and major projects in mergers and acquisitions and financial communications.

[2] MacKinnon first contested for a seat in parliament in the 2011 federal election in Gatineau, finishing third and almost 50 points behind Françoise Boivin, a former Liberal MP running for the New Democratic Party who secured 62% of the votes, and the then-incumbent Bloc Quebecois MP Richard Nadeau by just over 1 point.

Following the 2021 election, MacKinnon was appointed by Prime Minister Justin Trudeau as Chief Government Whip and was sworn in as a Privy Councillor.