As a young ensign Ernő Nagy fought in World War I, later joining the Magyar Atlétikai Club as an officer and fencer. He competed in both sabre and foil fencing, but at the international level achieved his best results with the sabre, including a sixth place in individual sabre at the unofficial 1933 World Championships. In the same year he won his only individual title at Hungarian Championships. In addition he was Hungarian Champion in team sabre in 1931-34 and 1936 and team foil in 1934. After the end of his active career in 1938 Nagy became head coach of the fencing division of his club.