Swimming at the 2020 Summer Olympics – Men's 100 metre breaststroke

The men's 100 metre breaststroke event at the 2020 Summer Olympics was held from 24 to 26 July 2021 at the Tokyo Aquatics Centre. It was the event's fourteenth consecutive appearance, having been held at every edition since 1968.

Summary
Great Britain's Adam Peaty defeated the field to become the country's first swimmer to claim back to back Olympic titles, and the second in this event after Japan's Kosuke Kitajima (2004-08). He jumped to an immediate lead, and never looked back, charging ahead of the field with his trademark high stroke rate to win gold in 57.37 - the fifth-fastest time in the history. The Netherlands' Arno Kamminga, the only other man in history to break the 58 seconds barrier, could not replicate his Dutch record from the heats and claimed silver in 58.00. Meanwhile, Italian Nicolò Martinenghi was only a shade off his national record time from the semi-finals, clocking a 58.33 to take bronze.

The U.S.' Michael Andrew was 7 tenths of a second shy of his American record set at the 2020 United States Olympic swimming trials, falling to fourth place in 58.84. Peaty's compatriot James Wilby (58.96) came fifth, while the U.S.' Andrew Wilson and China's Yan Zibei tied for sixth three one-hundredths behind in 58.99. Belarus' Ilya Shymanovich (59.36) was unable to break 59 seconds, rounding out the field in eighth.

The medals for the competition were presented by the United Kingdom's Sir Craig Reedie, IOC member, and the gifts were presented by Morocco's Zouheir El Moufti, FINA Bureau Member.

Records
Prior to this competition, the existing world and Olympic records were as follows.

No new records were set during the competition.

Qualification
The Olympic Qualifying Time for the event is 59.93 seconds. Up to two swimmers per National Olympic Committee (NOC) can automatically qualify by swimming that time at an approved qualification event. The Olympic Selection Time is 1:01.73. Up to one swimmer per NOC meeting that time is eligible for selection, allocated by world ranking until the maximum quota for all swimming events is reached. NOCs without a male swimmer qualified in any event can also use their universality place.

Competition format
The competition consists of three rounds: heats, semifinals, and a final. The swimmers with the best 16 times in the heats advance to the semifinals. The swimmers with the best 8 times in the semifinals advance to the final. Swim-offs are used as necessary to break ties for advancement to the next round.

Schedule
All times are Japan Standard Time (UTC+9)

Heats
The swimmers with the top 16 times, regardless of heat, advanced to the semifinals.

Semifinals
The swimmers with the best 8 times, regardless of heat, advanced to the final.