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

[1][2] Ariarne Titmus overcame a .62-second deficit in the last 50 metres to defeat defending champion Katie Ledecky.

This was Ledecky's first loss in a major international 400 metre freestyle competition.

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

The heats were held at 11:22.