In 2004, Sullivan became the first South Australian rider to win the Australian Championship since John Boulger in 1973 when he won the first year that the championship was run as a series (held over 3 rounds), rather than the single meeting format that had been in place since the first running of the title in 1926. Sullivan was undefeated over the three rounds held at the Gold Coast, Gosford and Olympic Park speedways. He defeated defending champion Leigh Adams who finished 2nd in all three rounds, with 1990 World #3 Todd Wiltshire finishing in third with 2 fourth and 1 third placings. This would prove to be Sullivan's only Australian Championship win and the final time he stood on the podium of the event.