At the Tokyo Olympics, Guy swam the second leg in the final of the men's 4 × 200 metre freestyle relay, and won his first Olympic gold with Tom Dean, Duncan Scott, and Matt Richards in a time of six minutes 58.58 seconds. He then won a second gold, swimming the butterfly leg in the mixed 4 × 100 metre medley relay, and set a world record time of 3 minutes 37.58 seconds together with Kathleen Dawson, Adam Peaty, and Anna Hopkin.