At the 2012 United States Olympic Trials in Omaha, Nebraska, the qualifying meet for the 2012 Olympics, Larson made the U.S. Olympic team for the first time by winning the 100-meter breaststroke in a time of 1:05.92, ahead of favorite Rebecca Soni. At the 2012 Summer Olympics in London, she earned a gold medal by swimming for the winning U.S. team in the preliminaries of the 4×100-meter medley relay. At the final 100-meter breaststroke, Larson false started. However, it was determined there was a technical issue and she was allowed to compete. She finished in sixth place.