He served as a New Hampshire state representative from Hillsborough County, from 2001 until 2006, during which he served on the House Committees on Criminal Justice and Public Safety and State-Federal Relations and Veterans Affairs.
From 2008 to 2010, Sullivan served as a member of the Manchester Board of Aldermen from the city's downtown Ward 3.
He served for ten years as a member of the United States Army Reserve and the Army National Guard, including five years of service as a commissioned officer.
Sullivan won a seat on Manchester's Board of Aldermen on November 6, 2007.
He defeated incumbent Pat Long, a fellow Democrat, in the non-partisan municipal election.