On 27th July 2021, at the 2020 Summer Olympic Games in Tokyo, Dean won the gold medal in the 200m freestyle, with his teammate Duncan Scott winning the silver medal. He then won gold in the men's 4 × 200 metre freestyle relay together with James Guy, Duncan Scott, and Matt Richards in a time of six minutes 58.58 seconds. Dean became the first male British swimmer to win two gold Olympic medals at the same games in 113 years.