At the 2020 Summer Olympics held in Tokyo, Japan, Pieroni competed in the prelims and final of the 4x100-meter freestyle relay. In the final of the event, he won a gold medal swimming the second leg of the relay. He and all of his prelims and finals relay teammates, Brooks Curry, Bowe Becker, Caeleb Dressel, and Zach Apple, won gold for their efforts. It was the first medal Pieroni won swimming in the final of any event at the Olympic Games.