He previously served as the head coach of the Western Michigan Broncos men"s basketball team and the University of South Florida (USF) Bulls men"s basketball team He is a native of Birmingham, Alabama. McCullum was hired to coach the USF Bulls on April 18, 2003 by athletic director Lee Roy Selmon after serving as the head coach at Western Michigan University, where he compiled a 44–45 record.
He was fired from USF on March 9, 2007 after showing minimal progress with the Bulls, who ended the 2006-2007 season at 12–18.
He compiled a 40–76 record as head coach at South Florida. He went on to coach the Nigerian senior men"s national basketball team, leading them to a 4–1 record at the All-Africa Games.
He was then hired an assistant coach at the University of San Francisco for the 2007-2008 season before taking a year off coaching. In July 2009 he was hired as an assistant coach at the University of Central Florida under head coach Kirk Speraw, a position he held for one year before moving on for the 2010-2011 season as an assistant under Georgia Technical men"s basketball head coach Paul Hewitt.