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

The event was won by Hannes Kolehmainen of Finland, the nation's first Olympic marathon medal and victory; Kolehmainen received his fourth gold medal, having won the 5000 metres, 10,000 metres, and individual cross country in 1912.

Estonia (Jüri Lossmann's silver) and Italy (Valerio Arri's bronze) also won their first marathon medals.

Shizo Kanakuri of Japan, still considered a missing person in Sweden after disappearing during the 1912 Olympic marathon, competed.

The United States made its sixth appearance, the only nation to have competed in each Olympic marathon to that point.