Billy O'Sullivan was born in Ballygunner, County Waterford in 1968. He was educated locally and from an early age he showed a great interest in hurling. Billy won an U15 Munster Colleges with De La Salle College, Waterford. He played for a combined Fitzgibbon Cup teams from 1987-1989.
Billy plays his club hurling with his local Ballygunner team. He had some success at underage levels and in 1988 and 1989 he won two Under-21 County medal with the club. senior county medal with the club. Billy added senior county medals to his collection in 1992, 1995, 1996, 1997, 1999 and 2001. This last win was later converted into a Munster club hurling title. O'Sullivan won his seventh county championship title in 2005 playing in a 14th senior county final. Billy also won an All-Ireland Clubs Sevens medal in 1993.
Billy joined the Waterford hurling team in the early 1987 and made his debut versus Kilkenny in the 1st round of the 1987 National Hurling League.
Billy won a Railway Cup medal in 1992.
Billy is brother to the present Waterford inter-county hurler, Shane O'Sullivan.