Sullivan began his career playing junior football at St Kevin's College in 2010, playing for the school's U18 side from Year 10 through to Year 12.
In 2016, Sullivan joined St Kevin's Old Boys in the Victorian Amateur Football Association (VAFA).
[1] Transitioning to the Victorian Football League (VFL) in 2019, he signed with Footscray.
[3][4] Sullivan's strong VFL performance in 2023 culminated in finishing third in voting for the J. J. Liston Trophy, and being selected as captain in the 2023 VFL Team of the Year.
[5] Despite reportedly garnering interest from AFL clubs Essendon and the Western Bulldogs, Sullivan went undrafted, and worked as an electrician while continuing to vie for selection from a professional club.