In football, he played as a linebacker, registering 170 tackles (103 unassisted), 21.0 stops for loss, 6.0 quarterback sacks, five forced fumbles and two interceptions, including one returned for a touchdown as a senior.

He earned Parade magazine high school All-America and first-team All-Texas Class 5A honors following both his junior and senior seasons, and played in the first-ever U.S. Army All-American Bowl on December 30, 2000.

[3] Following his senior season, he was also recognized as the Big 12 Defensive Player of the Year, and received the Dick Butkus Award and Bronko Nagurski Trophy.

[12] Johnson started all 16 games of his rookie campaign in 2005 and made 95 combined tackles (72 solo), five pass deflections, two forced fumbles, and two sacks.

[15][16] On October 29, 2006, Johnson made five combined tackles and two sacks on quarterback Matt Hasselbeck in the Chiefs' 30–27 win against the Seattle Seahawks.

[20] On September 16, 2007, Johnson recorded seven combined tackles, a season-high two pass deflections, forced a fumble, and sacked quarterback Rex Grossman twice during a 20–10 loss at the Chicago Bears in Week 2.

[21] On November 11, 2007, Johnson collected a season-high 11 solo tackles, deflected a pass, forced a fumble, and made an interception in the Chiefs' 27–11 loss to the Denver Broncos in Week 10.

[18] On December 28, 2008, he collected a season-high 11 combined tackles (five solo) and a pass deflection in the Chiefs' 16–6 loss at the Cincinnati Bengals in Week 17.

[23] Johnson recorded 85 combined tackles (68 solo), six passes defensed, four forced fumbles, 1.5 sacks, and an interception in 14 games and 14 starts.

[13] On January 23, 2009, the Kansas City Chiefs fired head coach Herman Edwards after they finished with a 2–14 record in 2008 and did not qualify for the playoffs for the third consecutive season.

[25] Throughout training camp, Johnson competed for a job as a starting inside linebacker against Demorrio Williams, Corey Mays, Monty Beisel, and rookie Jovan Belcher.

Head coach Todd Haley named Johnson a backup inside linebacker to start the regular season, behind Demorrio Williams, Corey Mays, Monty Beisel, and Jovan Belcher.

[27][28] He appeared in the Kansas City Chiefs' season-opener at the Baltimore Ravens and recorded three solo tackles, a pass deflection, and returned an interception by quarterback Joe Flacco for a 70-yard gain during a 38–24 loss.

[31] On January 3, 2010, Johnson recorded six combined tackles, a season-high four pass deflections, and returned two interceptions for touchdowns during a 44–24 victory at the Denver Broncos in Week 17.

He intercepted a pass by quarterback Kyle Orton, intended for wide receiver Brandon Lloyd, and returned it 45-yards for the first touchdown of his career in the third quarter.

[32][33] He finished the 2008 season with 37 combined tackles (30 solo), five pass deflections, three interceptions, two touchdowns, a sack, and a forced fumble in 15 games and was limited to three starts.

[35][36] On October 24, 2010, Johnson made six combined tackles, three pass deflections, and returned an interception for a touchdown during a 42–20 win against the Jacksonville Jaguars.

[37] He returned an interception thrown by quarterback Todd Bouman, that was intended for tight end Eric Potter, for a 15-yard touchdown in the third quarter.

[37] Johnson started all 16 games in 2010 and recorded 121 combined tackles (95 solo), a career-high 16 pass deflections, four forced fumbles, one sack, an interception, and a touchdown.

[42] On December 13, 2011, the Kansas City Chiefs fired head coach Todd Haley after a 35–10 loss to the New York Jets made them fall to a 5–8 record.

Johnson started in all 16 games and made a career-high 131 combined tackles (104 solo), nine pass deflections, two sacks, two interceptions, and a forced fumble.

Crennel retained the base 3–4 defense and named Johnson and Javon Belcher the starting inside linebackers to begin the regular season.

[47] On December 31, 2012, the Kansas City Chiefs fired head coach Romeo Crennel after they finished fourth in the AFC West with a 4–12 record.

[13] On January 21, 2014, Johnson was selected as a late replacement for the 2014 Pro Bowl after San Francisco 49ers' NaVorro Bowman was unable to participate after tearing his ACL and MCL during the playoffs.

He started in the Kansas City Chiefs' season-opener against the Tennessee Titans and made four solo tackles before exiting in the third quarter of the 28–10 loss after tearing his Achilles tendon.

Johnson intercepted a pass thrown by quarterback Ryan Fitzpatrick, intended for running back Matt Forte, and returned it for a 55-yard touchdown in the fourth quarter.

On January 6, 2018, Johnson made eight combined tackles and sacked quarterback Marcus Mariota in the Chiefs' 22–21 loss to the Tennessee Titans in the AFC Wildcard Game.