Fennell started his coaching career as an assistant coach for Alameda High School.[2] In 2015, Fennell joined UT Permian Basin as an unpaid assistant coach.[3] In 2016, Fennell was promoted by UT Permian Basin to serve as the team's associate head coach.[4] Then in 2017, Fennell decided to make the jump to Division I joining the Portland State Vikings as an assistant coach.[5] Fennell's next stop would be with the Louisville Cardinals in 2018 as he was as the team's director of operations.[6] In 2021, the Louisville Cardinals decided to promote Fennell to serve as one of the team's assistant coaches.[7] In 2022, Fennell decided to join the BYU Cougars as an assistant coach for the team.[8] Heading into the 2024 season, Fennell got his first career head coaching job as he was hired by the UT Rio Grande Valley Vaqueros.[9][10]