The men's 400 metre freestyle was a swimming event held as part of the swimming at the 1920 Summer Olympics programme.

[1] It was the third appearance of the event.

A total of 22 swimmers from 11 nations competed in the event, which was held from Thursday, August 26 to Saturday, August 28, 1920.

These were the standing world and Olympic records (in minutes) prior to the 1920 Summer Olympics.

The fastest two in each heat and the fastest third-placed from across the heats advanced.