The men's 800 metres was a track and field athletics event held as part of the athletics at the 1912 Summer Olympics programme. It was the fifth appearance of the event, which is one of 12 athletics events to have been held at every Summer Olympics. The competition was held from Saturday, July 6, 1912, to Monday, July 8, 1912. Forty-seven runners from 16 nations competed. NOCs could enter up to 12 athletes. The event was won by Ted Meredith of the United States, the nation's third consecutive victory in the 800 metres. Mel Sheppard became the first man to win two medals in the event, coming in second to miss out on defending his 1908 gold. Ira Davenport completed the United States sweep, the second time the Americans had swept the 800 metres podium.

The 800 metres, or meters, is a common track running event. It is the shortest commonly run middle-distance running event. The 800 metres is run over two laps of an outdoor (400-metre) track and has been an Olympic event since the first modern games in 1896. During the winter track season the event is usually run by completing four laps of an indoor 200-metre track.