Marcoux established himself as one of the brightest young stars in para-alpine skiing at the Sochi 2014 Paralympic Games. At age 16 (the youngest member of the team), he and his guide at that time, Robin Fémy, raced to a gold in the giant slalom and won bronzes in both the downhill and super-G. Marcoux originally skied with his older brother, Billy Joe, as his guide, but Billy Joe suffered a back injury just prior to the Sochi 2014 Paralympic Games, so Robin Fémy stepped in to guide Mac in Sochi. As a 20-year-old in Sochi, Russia, Mac Marcoux and his guide Jack Leitch won the downhill gold and bronze in the giant slalom at the 2018 Paralympic Winter Games.