While head coach at UNT from 1946-1966, Mitchell earned a record of 122–85–9. From 1946 to 1952, the Mean Green enjoyed six consecutive winning seasons, a UNT record. His teams earned 10 conference championships and played in three bowl games. In his 1966 season, North Texas went 8–2, which helped earn him National Coach of the Year honors. In 1986, he was inducted into the Texas Sports Hall of Fame.