In her first individual race at the 2020 Olympics, the prelims of the 100-meter freestyle on day five of competition, Weitzeil ranked eleventh for all prelims heats with her time of 53.21 and advanced to the semifinals. In the semifinals of the event, Weitzeil lowered her time to a 52.99 and qualified for the final ranked seventh overall. Weitzeil swam the freestyle leg of the 4x100-meter mixed medley relay in the prelims heats on day six, participating in the first swimming race in the history of the Olympic Games that men and women competed in the same event. She helped the relay finish ranked second overall and advance to the final.