[5] After experimenting with different sports, Warner began playing football when he was seven, which both he and his mother have cited as helping to shape his teenage years by giving him a sense of community.

[5] Though he admired numerous San Diego Chargers players, Warner grew up as a fan of the Dallas Cowboys along with his father.

He finished 13th among all linebackers in the 40-yard dash, eighth in the bench press, ninth in the short shuttle, and sixth in the three-cone drill.

[8][9] Warner attended pre-draft visits and private workouts with multiple teams, including the San Francisco 49ers, Broncos, and Buffalo Bills.

[10][11][12] At the conclusion of the pre-draft process, Warner was projected to be a second round pick by the majority of NFL draft experts and scouts.

[23] In the regular-season finale, he collected a season-high 14 combined tackles (nine solo) in a 48–32 road loss to the Los Angeles Rams in Week 17.

[24] Warner started all 16 games during his rookie year and recorded 124 combined tackles (85 solo), six pass deflections, and one forced fumble.

[30] During Week 16 against the Rams, Warner recorded 11 tackles and an interception off a pass thrown by Jared Goff, which he returned 46 yards for his first NFL touchdown in a narrow 34–31 victory.

[31] During Super Bowl LIV against the Kansas City Chiefs, Warner recorded seven tackles and intercepted a pass thrown by Patrick Mahomes during the 31–20 loss.

[49] In Week 5 of the 2023 season, against the Dallas Cowboys, Warner made a team-leading eight solo tackles, one interception, one forced fumble (on running back Tony Pollard), and a sack on quarterback Dak Prescott.

[54][55] In the 2023 season, Warner had 2.5 sacks, 132 total tackles (82 solo), four interceptions, 11 passes defended, and four forced fumbles in 17 games and starts.

[57] In the 49ers' season debut against the New York Jets, Warner posted 7 overall tackles, as well as a forced fumble which would be recovered by 49ers DL Maliek Collins.

[2] Warner's younger brother, Troy, followed him to BYU in 2015 as a defensive back[60] and is currently a member of the Tampa Bay Buccaneers practice squad.