Burnett attended both Carson High School (Carson, California) and Dominguez High School (Compton, California), actually graduating from Carson. He was a member of the 1999 Prep Star All-American team, a second-team All-State choice, and a member of the "Best of the West" by the Long Beach Press-Telegram. He played safety and running back while helping lead his team to two consecutive playoff appearances.
He went on to play for the University of Tennessee where he was switched from safety to linebacker. In 2002, he was lost for the year after suffering a torn anterior cruciate ligament in his left knee during the season opener. In 2003, as a junior he was named honorable-mention All-SEC and along with Michael Muñoz, became the first Vols juniors since 1944 to serve as team captains. In 2004, he received first team All-SEC and All-American honors. Burnett was also a semi-finalist for the Dick Butkus and Chuck Bednarick Awards.
Burnett was selected by the Dallas Cowboys in the second round (42nd overall) of the 2005 NFL Draft. He played sparingly as a rookie, after having problems with injuries in both of his knees. He was placed on the injured reserve list on December 29, after tearing his right ACL during a practice.
In 2006, he posted 40 tackles (29 solo), one sack, one interception and 2 forced fumbles. The next year, he registered 53 tackles (46 solo), 2 passes defensed and one forced fumble. In 2008, he finished with 38 tackles (29 solo), 2 sacks and 3 passes defensed.
During his time with the Cowboys he proved to be a quality backup (he only started 4 games), that was valuable as a coverage linebacker and special teams player. Burnett played mostly in the nickel and dime defense.
On March 10, 2009, he signed as a free agent with the San Diego Chargers, looking to become a starter. He played in 11 games (7 starts), posting 66 tackles (49 solo), 2.5 sacks and one pass defensed. The next year, he started every game at inside linebacker, finishing with 95 tackles (80 solo), 6 sacks, 2 interceptions and 2 forced fumbles.
On July 29, 2011, he signed as a free agent with the Miami Dolphins. He started every game and registered 105 tackles (second on the team) and 2.5 sacks. In 2012, he had career-highs with 110 tackles (80 solo) and 5 passes defensed. After the team signed free agents Philip Wheeler and Dannell Ellerbe, he was released on March 12, 2013.
Burnett signed with the Oakland Raiders on March 17, 2013. He started all 16 games at weakside linebacker, finishing with 129 tackles, 2.5 sacks and one interception. With his brother Kaelin, they became the first set of brothers in franchise history to play in the same regular-season game. After not being able to recover from an injured ankle he suffered in the second organized team activities session, he was waived on July 24, 2014.
KeyGP: games played
COMB: combined tackles
TOTAL: total tackles
AST: assisted tackles
FF: forced fumbles
FR: fumble recoveries
FR YDS: fumble return yards
IR YDS: interception return yards
AVG IR: average interception return
LNG: longest interception return
PD: passes defensed
Burnett is the cousin of Amir Johnson, who plays forward for the National Basketball Association's Philadelphia 76ers. His brother Kaelin Burnett played linebacker for the Tennessee Titans of the NFL.
He is a member of the Omega Psi Phi fraternity, initiated Spring 2004 via Iota Beta chapter.