Ian O’Brien was the world’s top breaststroker in the mid-1960s. In 1962 and 1966 he won both breaststroke events at the British Empire and Commonwealth Games, adding a fifth gold medal in the medley relay in 1962. O’Brien won gold in the 200 breaststroke at the 1964 Tokyo Olympic, defeating his great rival, American Chet Jastremski, and also earning a bronze medal in the medley relay with the Australian team. His Tokyo gold was won in world record time, his only world record. During his career, O’Brien won nine individual and six relay titles at the Australian Championships, despite retiring at age 21, after his appearance at the 1968 Olympics, where he failed to medal.
O’Brien later worked in television in Australia, and in 1979 started Videopak, a television documentary company. He was inducted into the Sport Australia Hall of Fame in 1986, and in 2000, was awarded the Australian Sports Medal. O’Brien was inducted into the International Swimming Hall of Fame in 2017.