After having gained his motor mechanic qualifications at age 19, Sullivan was regarded one of the best young riders in Australia, going on to win three South Australian Championships in succession in 1995, 1996 and 1997, and the Australian Under-21 Championship in 1993 and 1996 (the championship was not held in 1994 or 1995). Other than his 1993 Under-21 title which was won at the Olympic Park Speedway in Mildura, his 1996 U/21 title and his state title wins came at his home track, the North Arm Speedway. As North Arm closed at the end of the 1997 season, Sullivan is the last rider to win the SA Championship at the track.