Sullivan has also served on numerous local, regional, and statewide boards and commissions. Most recently he served on the Fairfax Park Authority Board. He has also served on the Northern Virginia Transportation Advisory Commission, the Fairfax Housing and Redevelopment Authority, the Fairfax Consumer Protection Commission, the Dranesville Budget Taskforce, and on the Virginia Commission for Civics Education. Sullivan is also the former president of Northern Virginia Legal Services, an organization that provides free counsel to low-income residents. Sullivan also serves on the Advisory Board of the University of Virginia's Sorensen Institute for Political Leadership.