The men's 400 metres event was part of the track and field athletics programme at the 1920 Summer Olympics.

The only returning finalist from the pre-war 1912 Games was Ted Meredith of the United States, who had finished 4th in Stockholm and who had broken the world record in 1916.

[2] Czechoslovakia, Egypt, Estonia, Finland, India, Luxembourg, and Spain appeared in the event for the first time.

The United States made its sixth appearance in the event, the only nation to compete in it at every Olympic Games to that point.

Again, the top three runners in each semifinal heat advanced, making a six-man final.