Garfield “Gary” Walter McMahon was originally from Manitoba and became interested in competitive handgun shooting soon after he joined the Atlantic Marksmen Association in 1957. His talent rocketed him to the Canadian Open Handgun Championship the next year. McMahon became the first Canadian to win this championship, which was previously held by visiting American shooters.

Nationally, McMahon won the Canadian Open three times and the Canadian Closed five times. He spent a decade representing Canada at numerous international events and at the 1959 Pan-Am Games in Chicago he won a bronze medal. The first time the Mayleigh Cup had been wrested away from the Americans, McMahon was present as a team member.

At the 1960 Rome Olympics he placed 10th and then placed fifth at the 1962 World Championships in Cairo. At the 1963 Pan American Games in Brazil McMahon won bronze and silver medals in individual competitions as well as two team silver medals.

His outstanding career came to a close with a 12th place finish at the 1964 Olympics, a bronze medal at the 1966 Commonwealth Games and a silver team medal in Columbia at the 1971 Pan Am Games. Gary McMahon was inducted into the Nova Scotia Sport Hall of Fame in 1982.