As a teenager, he won the Welsh Amateur Boxing Association title before being selected to represent Great Britain at the 1972 Summer Olympics in Munich.
He won his first bout at the Games before suffering a defeat to eventual silver medallist, Ugandan Leo Rwabwogo.
[1] He was selected to represent Wales as a teenager and fought Johnny Owen in the 1974 Welsh Amateur Boxing Association Championship, winning a controversial judges' decision.
[4] O'Sullivan was chosen to represent Great Britain in the men's flyweight boxing event at the 1972 Summer Olympics in Munich.
[1] Rwabwogo had won a bronze medal at the previous games, the 1968 Summer Olympics in Mexico, having reached the semi-finals of the competition.