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.
After a one-year stint with the Jaguars, McCullum moved on to Samford for the 1984 season before returning to South Alabama, where he stayed as an assistant until 1987.
He then joined the staff at Southern Illinois from 1988 to 1989 before becoming an assistant coach under Lon Kruger at Kansas State in 1990.
In 2000, McCullum was named the head coach at Western Michigan where he compiled a 44–45 record in three seasons, including a berth in the 2003 NIT.
McCullum was hired as the head men's basketball coach at South Florida on April 18, 2003, by athletic director Lee Roy Selmon.