The competition exists out of three rounds, each with races of up to nine athletes. In the first round, the sixteen fastest athletes qualify for the semifinals. In the semifinals, the two fastest athletes of each race, as well as the four fastest non-qualifiers advance to the final. The fastest competitor in the final is the winner of the event.
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Seventeen athletes qualified for the event with Zhang Yufei and silver medalist at the most recent world championships Hali Flickinger as the two main medal contenders, though with a small field, anything could happen. Boglarka Kapas was the reigning world champion, but Regan Smith, multi-medalist Katinka Hosszu, and Yu Liyan were definitely not to be counted out. Other medal contenders and potential outsiders also included Laura Stephens, Brianna Throssell, Suzuka Hasegawa, and fourth-place finisher at the world championships Franziska Hentke.
Defne Tacyildiz was the youngest athlete in the field at the age of 18, as she was a year younger than Regan Smith and three years younger than Helena Bach, Yu Liyan, and Suzuka Hasegawa, with Hasegawa the only of the five to have competed at the Olympic Games before. The most experienced athlete in the field was Katinka Hosszu, who would be competing at her fifth Olympic Games at the age of 32. She was a month older than Franziska Hentke, who made her Olympic debut in 2016, and a year older than Alys Margaret Thomas, who made her Olympic debut.
Zhang Yufei won the event in a new Olympic record, winning her second Olympic medal after her silver medal in the 100 metres butterfly. Regan Smith also won her second Olympic medal, after winning the bronze medal in the 100 metres backstroke, in which she recorded Olympic records in the heats and the semifinals. Bronze medalist Hali Flickinger also won her second Olympic medal, having won the bronze medal in the 400 metres individual medley a few days prior. Boglarka Kapas missed out on the medals by almost a second, after she had won a bronze medal in the 800 metres freestyle in 2016, with Svetlana Chimrova, Yu Liyan, and Alys Margaret Thomas in a close battle for the places behind her. Brianna Throssell completed the final while Suzuka Hasegawa missed out on qualification for the final by three-tenths of a second.
