Sullivan took to his first season with the Wildcats in 1999–2000, on his debut chipping in with three rebounds and tough defense in seven minutes against Lafayette, and later the freshman converted his first career points with a 3-point shot from the top of the key in the first half against Fairleigh Dickinson. He tied a career high with seven points in 12 minutes in 67–66 loss to Miami on 17 January 2000 and three days later grabbed five rebounds and scored five points in 66–57 win at Providence. Overall it was a successful rookie season for the Englishman, in which another highlight unfolded when he made several spectacular plays in 86–69 win over Notre Dame, ending the night with seven points and five rebounds in 14 minutes of activity. By the end of the season, Sullivan had played 29 games, averaging 2.31 PPG.