As a true freshman at Pittsburgh in 2018, Hallett redshirted.[2] The following year, he appeared in 12 games, starting one, and recorded 14 tackles with two pass breakups.[2] In 2020, he played ten games, starting the final four, and tallied 30 tackles, two of which were for a loss, four pass breakups and two interceptions.[4][5] Hallett was named honorable mention all-conference in 2021 after starting all 14 games and making 70 tackles, 2.5 TFLs, nine pass breakups, three interceptions and two forced fumbles.[4] In his final year, he started all 13 games and earned second-team all-conference honors while posting 54 tackles, four TFLs and nine pass breakups with two forced fumbles, additionally being a semifinalist for the Jim Thorpe Award, given to the best defensive back nationally.[4][6]
Hallett was selected by the Jacksonville Jaguars in the sixth round (208th overall) of the 2023 NFL draft.[9] He was waived on August 29, 2023, and re-signed to the practice squad.[10][11] He signed a reserve/future contract on January 8, 2024.[12]
On August 27, 2024, Hallett was waived by the Jaguars.[13]