The men's 400 metres hurdles event at the 2020 Summer Olympics took place between 30 July and 3 August 2021 at the Olympic Stadium. 36 athletes from 26 nations competed.
In what has been described as one of the greatest races in Olympic history, Karsten Warholm of Norway won the gold medal, setting a new world record of 45.94 seconds. He beat his own previous record, set a month before, by 0.76 seconds; silver medalist Rai Benjamin of the United States beat the previous record by 0.53 seconds. Brazilian hurdler Alison dos Santos took bronze and would have bettered the almost 30-year-old Olympic record in the final by 0.06 seconds. The medals were the first ever in the event for both Norway and Brazil; the United States' podium streak in the event stretched to four Games.