 On September 24, 2016, Marin was named the Progressive Conservative candidate for the November 2016 by-election in Ottawa—Vanier.He was defeated by Liberal candidate Nathalie Des Rosiers by a 19-point margin, the best performance by a Progressive Conservative candidate in the riding for fifty years.In remarks given after his defeat, Marin warned that party leader Patrick Brown had to put social conservatives "in their place" because they are "a threat to the party" that might cost them the 42nd Ontario general election.