At the 2012 U.S. Olympic Trials in Omaha, Nebraska, the qualifying meet for the U.S. Olympic team, McGill placed second in the 100-meter butterfly event with a time of 51.32 seconds, just behind Michael Phelps and just ahead of Ryan Lochte. At the 2012 Summer Olympics in London, McGill placed sixth the 100-meter butterfly, and earned a gold medal by swimming in the preliminaries for the winning U.S. team in the 4×100-meter medley relay.