The Cowboys (10-2, 6-2 Big 12) were picked to finish at the bottom of the division but instead set a new school record with 10 regular-season wins and shared the South title with Oklahoma and Texas A&M.
Gundy received 12 of 20 first-place votes from The Associated Press' panel.
Texas A&M's Mike Sherman got seven votes after a midseason turnaround helped the Aggies win their final six games and earn their share of the division title. Art Briles received the remaining vote after leading Baylor to bowl eligibility for the first time since 1994.
Gundy was also named the Big 12 coach of the year Tuesday in voting by the league's coaches.