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. At the 10th Canadian Screen Awards in 2022 he received two nominations for his film The Righteous, for both Best Supporting Actor and Best Original Screenplay.