Barrett was named Mountain West Conference Defensive Player of the Year as a senior in 2013 after ranking fifth in the nation with 12 sacks and 20.5 tackles for a loss.

[4] Barrett stated that his decision to choose to sign with the Denver Broncos was due to their willingness to look past draft rankings.

[5] Throughout training camp, Barrett competed for a roster spot as a backup linebacker against Steven Johnson, L. J. Fort, Jamar Chaney, Jerrell Harris, and Corey Nelson.

[6] On October 14, 2014, the Broncos promoted Barrett to their active roster after an injury to starting linebacker Danny Trevathan.

He was once again signed to the 53-man roster for the American Football Conference Divisional Playoff Game against the Indianapolis Colts, but did not play.

Head coach Gary Kubiak named Barrett the third string strongside linebacker to begin the regular season, behind Von Miller and Lerentee McCray.

[10] During a Week 6 26–23 overtime road victory over the Cleveland Browns, Barrett made his first NFL start after DeMarcus Ware suffered a back injury.

[20] With his strong performance, Barrett earned National Football Conference (NFC) Defensive Player of the Week honors.

[22] The following week, Barrett recorded his first NFL interception and a strip-sack on Jared Goff which was returned for a touchdown by teammate Ndamukong Suh in a 55–40 road victory over the Los Angeles Rams.

[25] Barrett finished the 2019 season setting new career highs with a league leading 19.5 sacks, 58 tackles, six forced fumbles, two pass deflections, and an interception in 16 games and starts.

[29] During a Week 3 28–10 road victory over his former team, the Broncos, Barrett had six total tackles and two sacks which included his first career safety on quarterback Jeff Driskel.

[30] In Week 9 against the New Orleans Saints on Sunday Night Football, Barrett recorded four tackles and a strip-sack on Drew Brees that was recovered by the Buccaneers during the 38–3 loss.

[31] Three weeks later against the Kansas City Chiefs, Barrett recorded a strip-sack on Patrick Mahomes that was recovered by the Buccaneers in the 27–24 loss.

[32] In Week 14 against the Minnesota Vikings, Barrett recorded two sacks on Kirk Cousins and four tackles as the Buccaneers won 26–14.

[35] Barrett finished the 2020 season with 57 total tackles, eight sacks, three passes defended, and two forced fumbles in 15 games and starts.

[36] He recorded five total tackles and sacked Aaron Rodgers thrice during the NFC Championship Game as the Buccaneers defeated the Green Bay Packers 31–26 to advance to Super Bowl LV.

[44] Two weeks later against the New England Patriots, Barrett recorded three tackles, a pass deflection, and a sack in the narrow 19–17 road victory.

[55] During a Week 8 27–22 loss to the Ravens, Barrett suffered a torn Achilles tendon, prematurely ending his season.

His biggest play of the season came against the Chicago Bears in Week 2 when he intercepted a pass from Justin Fields and returned it 4 yards for his first career touchdown, sealing a 27–17 win for the Buccaneers in the game's closing minutes.

[59] On July 20, 2024, Barrett announced via his Instagram account that he was retiring from the NFL, citing a desire to spend more time with his family.