Sonia O'Sullivan (born 28 November 1969) is an Irish former track and field athlete. She won a gold medal in the 5000 metres at the 1995 World Championships, and a silver medal in the 5000 metres at the 2000 Olympic Games. Her 2000Â m world record of 5:25.36, set in 1994 stood until 2017.
O'Sullivan first came to prominence when winning the 1500Â m at the 1991 Universiade, before going on to finish fourth in the 3000Â m final at the 1992 Olympic Games. She then won a silver medal in the 1500Â m at the 1993 World Championships. She was the favourite for the 5000Â m title at the 1996 Olympic Games but dropped out of the final due to illness. As well as her 1995 World title, she won three gold medals at the European Championships, in the 3000Â m (1994), 5000Â m (1998) and 10,000Â m (1998), and is a two-time World Cross Country Champion.