Marcus Dinwiddie was one of the youngest athletes to win a medal in Olympic shooting. He began shooting at the District of Columbia National Guard rifle range after they changed the regulations to allow civilians to use the facilities. After the 1924 Olympics, Dinwiddie enrolled at the University of Virginia and continued shooting as a member of the Monticello National Guard, with whose team he competed at several national championships. His only international honor, apart from his Olympic medal, came at the 1925 Internationals at Rheims, France when he won the English match.