Sullivan then transferred to Vermont where he provided reliable outside shooting to the defense-oriented Catamounts.[2] In taking advantage of an extra year of eligibility offered by the NCAA to athletes playing during the COVID pandemic, Sullivan returned to Vermont for a fifth season. He averaged a career-best 11.7 points per game, displaying a strong overall floor game (4.9 rebounds and 2.4 assists per game) and leading the Catamounts to America East regular-season and tournament championships.[3] At the close of his final year of eligibility, Sullivan was named first-team All-America East Conference and the America East Player of the Year.[4][5]