As a freshman in 2018, Sirmon totaled one tackle and a forced fumble.[3] In the 2019 Las Vegas Bowl, Sirmon recovered a fumble as the Huskies beat Boise State.[4] Sirmon finished the 2019 season with 28 tackles and two going for a loss, and a fumble recovery.[5] Sirmon had a career day in a win over Utah in 2020, where he racked up nine tackles and a fumble recovery.[6] Sirmon finished the shortened 2020 season with 27 tackles, 1.5 tackles for loss, and a fumble recovery.[7] In week nine of the 2021 season, Sirmon recorded his first career interception, picking a pass in the redzone by quarterback Tanner McKee, helping Washington beat Stanford 20–13.[8] Sirmon finished his breakout 2021 season with 91 tackles with four being for a loss, a pass deflection, an interception, a forced fumble, and a fumble recovery.[9] Sirmon entered the transfer portal following the season.[10][11]
California
Sirmon decide to transfer to California to continue his college career.[12][13] Sirmon started the 2022 season strong, as in week three he totaled 15 tackles with two going for a loss, and 1.5 sacks, but the Golden Bears fell to Notre Dame 24–17.[14] In week seven, Sirmon picked off a pass by Owen McCown, but California lost 20–13 against Colorado.[15] In week twelve, Sirmon recovered a fumble that he returned for a touchdown that would win the Golden Bears the game, as they would beat Stanford 27–20.[16] Sirmon finished the 2022 season as his best, tallying 104 tackles with six going for a loss, 3.5 sacks, four pass deflections, an interception, a fumble recovery, a forced fumble, and a touchdown.[17] For his performance, Sirmon was named a first-team all Pac-12 selection.[18] After the conclusion of the 2022 season, Sirmon announced that he would return to California for his final season.[19][20] Sirmon was named preseason first team all Pac-12, for the upcoming 2023 season.[21] Sirmon was also named as a preseason All-American by Athlon Sports.[22] Sirmon would also be named to multiple award watch lists, such as the Bronko Nagurski Trophy watch list, and to the Butkus Award watch list.[23][24]
Sirmon signed with the New York Jets as an undrafted free agent on May 3, 2024.[27] He was waived on August 27, and later re-signed to the practice squad.[28] He signed a reserve/future contract on January 6, 2025.[29]
