The men's 400 metre individual medley event at the 2024 Summer Olympics was held on 28 July 2024 at Paris La Défense Arena.

[1] The world record holder Léon Marchand of France was the heavy favourite going into the event.

He qualified for the finals with the fastest seed, while the USA's defending Olympic champion Chase Kalisz and Australia's defending Olympic bronze medallist Brendon Smith both failed to qualify for the finals.

Also in the heats, Germany's Cedric Büssing swam a time of 4:11.52 to break his country's national record.

[7] Leon Marchand qualified with the fastest seed in the second heat, while Carson Foster won the first.

[12] Léon Marchand led the race from start to finish, splitting the first 50 metres 0.65 ahead of his world record pace.

[13] Great Britain's Max Litchfield finished fourth for the third consecutive Olympics with a time of 4:08.85—a new national record.