McDorman was born John Allen McDorman IV in Dallas, Texas, the son of Deborah Gale (née Stallings) and John Allen McDorman III. He has a younger sister, Morgan, and an older half-sister, Mandy. After dropping out of the Boy Scouts of America to pursue his acting career, he booked his first job playing a Boy Scout in an industrial film about the importance of Scouting. McDorman studied acting at the Dallas Young Actors Studio and attended Richardson High School, Westwood Junior High and Northwood Hills Elementary in Texas.