Lashlee attended Shiloh Christian School in Springdale, Arkansas, where he played quarterback under head coachGus Malzahn. Lashlee posted a state record 40 career wins and led his team to three straight state championship games, winning two titles. Lashlee holds a number of Arkansas high school records.
Regarded as a three-star recruit by Rivals.com, Lashlee was ranked as the No. 19 pro-style quarterback in a 2002 class that also featured Ben Olson, Trent Edwards, Drew Stanton, and Matt Moore.
Prior to 2017, Lashlee had worked under Malzahn for his entire career with the exception of his one year at Samford University. From 2004 to 2005, Lashlee worked with the quarterbacks at Springdale High School. Following the announcement of Malzahn's hire as Arkansas Razorbacks offensive coordinator in 2006, Lashlee was hired as an offensive graduate assistant. Following this season, Malzahn left to become the offensive coordinator of the Tulsa Golden Hurricane football team. Although invited to join Malzahn's staff at Tulsa, Lashlee left coaching and remained in Northwest Arkansas. Instead, Lashlee and his brother in law wrote, published, and marketed High School SportsThe Magazine, a publication based on high school sports in Arkansas. During the two years Lashlee was involved in the business, he made relationships with high school coaches throughout Arkansas and marketed his magazine to distributors. Lashlee volunteered as quarterbacks coach at Har-Ber High School when his schedule would allow. Malzahn was hired as the offensive coordinator at Auburn for the 2009 season. Following this announcement, Malzahn offered Lashlee to join his staff as a graduate assistant, returning Lashlee to coaching. He remained in this role until leaving to become offensive coordinator and quarterbacks coach for Samford University Bulldogs in 2011. During his coaching season the team offensive improved in points per game, total offense, and improved their record from 4–6 to 6–5 through the installation of a high tempo offense. Malzahn left Auburn following 2011, becoming head coach of the Arkansas State Red Wolves. Lashlee followed, becoming offensive coordinator and quarterbacks coach for Arkansas State. Malzahn returned to Auburn as head coach after one year at Arkansas State. On December 6, 2012, Gus Malzahn named Rhett Lashlee as his offensive coordinator. In 2013, Lashlee was a finalist for the Broyles Award, given annually to the nation's top college football assistant coach. By 2016, however, head coach Malzahn had taken back the reins of the offense and as a result, Lashlee had less control of the offense. In 2017, Lashlee subsequently moved on to be UConn's offensive coordinator.
SMU
On January 4, 2018, it was reported that Lashlee was hired by SMU.
Miami
On January 3, 2020, it was reported that Lashlee had filled the offensive coordinator vacancy at the University of Miami.
