The women's marathon 10 kilometre event at the 2020 Summer Olympics was held on 4 August 2021 at the Odaiba Marine Park.

Ana Marcela Cunha won with a time of 1:59:30.8, becoming the first Brazilian woman swimmer to win a gold medal in the Olympics.

Former Olympic gold medalist Sharon van Rouwendaal of the Netherlands finished second, with Kareena Lee of Australia taking the bronze.

No preliminary heats are held, with only the single mass-start race being contested.

The race is held using freestyle swimming, with a lack of stroke regulations.