He competed for the United States in the 1912 Summer Olympics held in Stockholm, Sweden in the shot put where he won the gold medal. He also took part in the shot put (both hands) competition where the distance thrown with each hand was added together. This was the only time this event was held in the Olympic program, and McDonald finished second behind teammate Ralph Rose who had finished second to him in the shot competition.
McDonald returned 8 years later after World War I to compete in the 1920 Summer Olympics in Antwerp, Belgium. Here he won the gold medal in the 56 lb weight throw in the second and final time this competition was held in the Olympic program.