Mahoney's promotion was not enough for him to save his seat in the subsequent 1972 election, and he went down to defeat at the hands of Tory rival Peter Bawden, losing by more than 16,000 votes.[1] In 2011, Mahoney joked that the Liberals "will elect an MP in Calgary again before the Maple Leafs win the Stanley Cup."[1]
Subsequent to his defeat, Mahoney, a lawyer by training, was appointed to the Federal Court of Appeal.[1]
Mahoney joined the Calgary Stampeders of the Canadian Football League as an executive in 1955[2] and, in 1959, moved the Labour Day Classic match against the rival Edmonton Eskimos from Edmonton to Calgary, it has been played there ever since.[1] He briefly served as the team's general manager in 1965 and also served as president of the league's Western Football Conference.[2]