Mark O'Brien is a Canadian actor and director best known for his roles as Des Courtney in Republic of Doyle and Tom Rendon in Halt and Catch Fire. He won the Canadian Screen Award for Best Actor at the 8th Canadian Screen Awards for his performance as Terry Sawchuk in the biographical drama film Goalie.

Republic of Doyle is a Canadian comedy-drama television series set in St. John's, Newfoundland and Labrador, which aired on CBC Television from January 6, 2010, to December 10, 2014.