John Thomas Devitt, AM (born 4 February 1937) is an Australian former sprint freestyle swimmer of the 1950s and 1960s, who won a gold medal in the 100-metre freestyle at the 1960 Summer Olympics in Rome. He won in controversial circumstances, being awarded the gold medal despite the timekeepers recording a slower time than the American silver medallist Lance Larson. He also claimed a gold medal at the 1956 Summer Olympics in Melbourne, in the 4×200-metre freestyle relay.
Growing up just 250 metres from the Granville Olympic Pool, Devitt learnt to swim as part of the government-funded Learn to Swim program. He was educated first at Holy Family Primary School, The Trongate, Granville East, and later at Parramatta Marist High School in Parramatta. Both were Roman Catholic schools, where he also swum competitively for the school team. Devitt was initially trained by Tom Penny at the Clyde Swim Club, based at the Granville Pool, until it disbanded in 1947 and he moved to Manly Swim Club along with Penny. Devitt remains a member of the Swim Club. Penny often allowed his swimmers to train in warm waters by having them swim against the current of discharged water from a power plant. Devitt believed that such training gave him an advantage as it taught him to be unaffected by "rain, heat, currents or any other natural or unnatural variables".