McCullum got his start in coaching in the high school ranks before taking his first college coaching job at
South Alabama in 1983. 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. McCullum followed Kruger to
Florida where he was an assistant from 1991 to 1996, and once more worked under Kruger at
Illinois from 1996 to 2000. 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. In four seasons, McCullum was 40–76, and was fired after the 2006–07 season on March 9, 2007. After South Florida, McCullum coached the
Nigerian men's national basketball team where he led the team to a 4–1 record at the All-Africa Games. Following his coaching with Nigeria, McCullum joined the staff at
San Francisco for one season before moving on to be an assistant coach at
UCF under
Kirk Speraw. In 2010, McCullum became an assistant coach for the
Georgia Tech men's basketball team under head coach
Paul Hewitt. After Hewitt was fired, McCullum was not retained and became an assistant for the
Guangzhou Long-Lions of the
Chinese Basketball Association before joining
Dana Altman's staff at
Oregon as an assistant coach. McCullum was named head coach at Florida A&M on May 16, 2017. ==Head coaching record==