The Men's 400 metre freestyle competition at the 2019 World Championships was held on 21 July 2019.

[1][2] The three-time defending champion was Sun Yang, and he successfully defended his title for a record-breaking 4th consecutive victory in the world championships in this event.

[3] He became the third man to win an event 4 times at the world championships after Grant Hackett in the 1500 meter freestyle and Ryan Lochte in the 200 meter individual medley.

[4] Prior to the competition, the existing world and championship records were as follows.

The heats were held at 10:16.