At the 2012 Summer Olympics in London, Soni won her inaugural medal, a silver, in the 100-meter breaststroke, finishing 0.08 seconds behind 15-year-old Lithuanian Rūta Meilutytė and repeating her result from the 2008 Olympics. After topping the heats of the 200-metre breaststroke with a time of 2:21.40, and breaking Annamay Pierse's world record in the semi-finals with a time of 2:20.00, Soni won a gold medal in the final of the 200-meter breaststroke with a time of 2:19.59, breaking her own world record and becoming the first woman ever to break 2 minutes 20 seconds in the event. With her win, Soni became the first female to successfully defend her title in the event. In her final event, the 4×100-meter medley relay, she won gold with Missy Franklin, Dana Vollmer and Allison Schmitt. Swimming the breaststroke leg, she recorded a time of 1:04.82, and the U.S. team went on to set a new world record with a time of 3:52.05, bettering the previous Chinese-owned record of 3:52.19 set in 2009.