[4] He later attended Brebeuf Jesuit Preparatory School[5] in Indianapolis, where he played football, basketball, and ice hockey.

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, offensive coordinator Jim Chaney and he 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.

[7] 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 2011, Sumlin coached Houston to a 12–0 start before losing the Conference USA Championship Game to the Southern Miss Golden Eagles.

[11] On December 10, 2011, Sumlin told his players he was leaving Houston, effective immediately, to accept a job at another school.

[12] KRIV in Houston and ESPN's Joe Schad both reported that Sumlin was to become the new coach at Texas A&M University.

[15] Manziel went on to win the Heisman Trophy and Sumlin took Texas A&M, in their first year in the Southeastern Conference, to an 11–2 record, including victories over then No.

[21][22] On January 6, 2022, Sumlin was named the head coach and general manager for the Houston Gamblers of the United States Football League.