In the 1908 Summer Olympics, 1500 m competition, Sullivan won his first-round heat with a time of 4:07.6, winning a closely contested heat, defeating defending champion James Lightbody. In 1909 Sullivan won the three-mile Canadian Championship held at Montreal, and pulled two tendons in his right ankle, which put him out of competition for the indoor season of 1909–1910. Sullivan was using swimming as a non-impact physiotherapy training when he was advised to compete in a triathlon once rehabilitated. He competed in a few triathlons, placing well in the triathy, but had a recurrence of the tendon problem and had to retire from sport altogether. As well as being an athlete Sullivan was known to have an interest in Pool and Billiards, winning The Manly Cup in its inaugural year.