Johnson was signed by the Philadelphia Eagles as an undrafted free agent in 2011 and would play in the NFL for six seasons with the Eagles, Pittsburgh Steelers, Seattle Seahawks, Chicago Bears, Baltimore Ravens and Dallas Cowboys.
[1] During the 2007 football season Johnson backed up junior Stephen McGee at quarterback.
During fall camp Johnson competed for the starting job with senior Stephen McGee, but lost out to the veteran team leader.
In the second game of the season, vs New Mexico, Stephen McGee suffered a right shoulder sprain on the opening series.
[3][4] He returned to the wide receiver position against Army, but McGee re-injured his shoulder during the game, paving the way for Johnson to step in and lead Texas A&M to a victory.
[9] Johnson led the team to a 6–6 regular-season record including an upset road win at Texas Tech.
[10] In the 2009 Independence Bowl against Georgia, he completed 29 of 58 passes for 362 yards and two touchdowns, but was sacked three times and intercepted twice in the loss.
[11] He entered the 2010 season as the Preseason Big 12 Offensive Player of the Year and a dark horse Heisman Trophy candidate.
[13] During the ensuing Kansas game, he split time at quarterback with second-string Ryan Tannehill.
[14][15][16] However, during the Kansas game, he raised his total career yardage to 8,888, breaking the school record of 8,876 held by Reggie McNeal from 2002 to 2005.
[21] A sports editor commented that Johnson had the least zip of all the quarterbacks who played, and did not throw like he used to during the 2009 season.
Johnson signed with the Sacramento Mountain Lions in September 2012, serving as the team's backup quarterback.
In 2019, Johnson joined the Indianapolis Colts under the Bill Walsh Diversity Coaching Fellowship.
[31] Johnson was part of the staff that led the Texans to a 10–7 regular season finish, the AFC South title, and a Wild Card Round victory over the Cleveland Browns and Johnson helped guide and develop rookie quarterback C. J. Stroud in 2023, who went on to win NFL Rookie of the Year.
Their father, Larry Johnson, who also played for the Aggies, died of a stroke in December 2007.