Sumlin served as an assistant coach at Washington State, Wyoming, Minnesota, and Purdue ; served as assistant head coach at Texas A&M for two years under R.C. Slocum; and for five years at Oklahoma under Bob Stoops, serving the last two years as co-offensive coordinator. In addition to Stoops and Slocum, he has served as an assistant coach under Mike Price at Washington State and Joe Tiller at Purdue. While at Purdue, he and offensive coordinatorJim Chaney aided Tiller in implementing the then-uncommonly used spread offense, and the Boilermakers, with Drew Brees as starting quarterback, broke a string of Big Ten passing records and made a surprise run to the 2001 Rose Bowl, Purdue's first Rose Bowl in three decades. He left for Texas A&M to serve as the offensive coordinator and assistant head coach for two seasons before joining the University of Oklahoma. In his final year with the Oklahoma Sooners, Sumlin's offense was one of the best in the country, averaging 44 points per game. In December 2009, it was announced that Sumlin was a finalist for the Paul "Bear" Bryant Award. In 2011, Sumlin coached Houston to a 12–0 start before losing the Conference USA Championship Game to the Southern Miss Golden Eagles. On December 10, 2011, Sumlin told his players he was leaving Houston, effective immediately, in order to accept a jobat another school. KRIV in Houston and ESPN's Joe Schad both reported that Sumlin was to become the new coach at Texas A&M. Special teams coordinatorTony Levine coached Houston in the 2012 TicketCity Bowl. In 2012, Sumlin named quarterback Johnny Manziel his starter. Manziel would go on to win the Heisman Trophy and Sumlin would take Texas A&M, in their first year in the Southeastern Conference, to an 11–2 record, including victories over then #1 Alabama in Tuscaloosa, and #11 Oklahoma in the AT&T Cotton Bowl. The Aggies finished the 2012 season ranked in the top 5 of both the Coaches Poll and the AP Pollfor the first time since 1956. Texas A&M would also lead the SEC in total offense, total scoring offense, total rushing yds, and led the nation in third down conversion percentage. Sumlin and the Aggies would become the first SEC team in history to amass over 7,000 yds in total offense. Coach Sumlin was the first head coach to win more than eight games in his first season as head coach. On November 30, 2013, Sumlin agreed to a new six-year contract as head coach at Texas A&M. The contract, valued at $30 million over six years, was guaranteed. If Texas A&M had fired him after the 2015 and 2016 seasons, the buyout amounts would have had to be paid out within 60 days of termination. On November 21, 2017, news outlets reported that Sumlin would be fired following the 2017 season finale against LSU. On November 26, 2017, Sumlin was fired after six seasons. He compiled a 51–26 record during his tenure. Despite never posting a losing record as the coach of A&M, he only won more than nine games once, and only had one winning record in SEC play. Sumlin received a $10.4 million buyout under the terms of his contact, and was replaced by Jimbo Fisher for the 2018 season. On January 14, 2018, Sumlin was hired as the University of Arizona's head coach.
