The women's 400 metres hurdles event at the 2020 Summer Olympics took place between 31 July and 4 August 2021 at the Japan National Stadium.

[2] At the U.S. Olympic trials in June 2021, Sydney McLaughlin became the first woman to run the event in under 52 seconds, improving Dalilah Muhammad's world record of 52.16 secs to 51.90.

Dutch athlete Femke Bol broke the European record with 52.03 for the bronze, to move to third on the world all-time list.

McLaughlin was also in the Rio Olympics, but then she made news for qualifying for the semi-final round a few days after her seventeenth birthday.

In 2021 at the United States Olympic Trials, she reversed that picture by winning with a new world record of 51.90.

Knowing she had to run a world record, Muhammad was out fast clearing the first hurdle just ahead of McLaughlin and Bol.

Those three separated from the rest of the field but kept the same pattern, Muhammad, McLaughlin, Bol over all ten hurdles.

Due to the COVID-19 pandemic, the period was suspended from 6 April 2020 to 30 November 2020, with the end date extended to 29 June 2021.