Dr. McMullen received his M.D. degree from Texas A&M College of Medicine in 1986, and did his surgical residency at the prestigious Alton Ochsner Clinic and Hospital in New Orleans, Louisiana, from 1986 to 1991. He served as Chief Resident during his final year, receiving many honors as well as publishing several research articles on various surgical topics while he was in residency there.

Dr. McMullen joined the staff of Integris Southwest Medical Center (formerly South Community Hospital) in 1991 and has been in private practice in Oklahoma City ever since.