McMahon signed with the Toronto Argonauts on May 3, 2023.[3] Following training camp, he began the 2023 season on the practice roster, but made his professional debut on September 15, 2023, against the Montreal Alouettes, where he recorded two carries for 30 yards and one reception for two yards.[4] Following injuries to fellow running backs A. J. Ouellette and Andrew Harris, McMahon earned his first career start on September 23, 2023, against the Hamilton Tiger-Cats.[5] He finished the year having played in seven regular season games, starting in one, where he had 38 carries for 134 yards and three touchdowns along with 10 catches for 64 yards.[6]