The men's 100 metre backstroke event at the 2020 Summer Olympics was held from 25 to 27 July 2021 at the Tokyo Aquatics Centre.

This time, 2016 Olympic bronze medalist and 2019 World Championship silver medalist Evgeny Rylov edged his compatriot Kliment Kolesnikov and defending Olympic champion and world record holder Ryan Murphy, who did not medal in 2019, to win first gold by a Russian in this event and also the first gold medal in swimming by a Russian since Larisa Ilchenko won the open water competition in 2008.

Meanwhile China's two-time defending World champion Xu Jiayu (52.51) fell to fifth, while Spain's Hugo González (52.78) edged Australia's Mitch Larkin (52.79) by one one-hundredth of a second to take sixth.

Up to two swimmers per National Olympic Committee (NOC) could automatically qualify by swimming that time at an approved qualification event.

Up to one swimmer per NOC meeting that time was eligible for selection, allocated by world ranking until the maximum quota for all swimming events is reached.