He played college football for the California Golden Bears, and was signed as an undrafted free agent by the Carolina Panthers in 2005.

Alexander was also a member of the Baltimore Ravens, Washington Redskins, Arizona Cardinals, Oakland Raiders, and Buffalo Bills.

Alexander went to Saint Mary's College High School, where he played as a defensive lineman for the Panthers football team.

[8] Throughout training camp, Alexander competed for a roster spot against Atiyyah Ellison, Kris Jenkins, Charles Hill, and Eddie Freeman as a backup defensive tackle.

[9] On September 3, 2005, the Carolina Panthers waived Alexander as part of their final roster cuts, but signed him to their practice squad two days later.

[10][16] Head coach Joe Gibbs named Alexander the fifth defensive tackle on the Redskins’ depth chart to start the regular season, behind Cornelius Griffin, Kedric Golston, Anthony Montgomery, and Ryan Boschetti.

On January 5, 2008, Alexander appeared in his first career playoff game as the Redskins lost 35–14 at the Seattle Seahawks in the NFC Wild Card Round.

[23] Throughout training camp, Alexander competed for a roster spot as a backup defensive tackle against Matthias Askew, Ryan Boschetti, and Jonathan Mapu.

[24][25] Head coach Jim Zorn named Alexander the fourth backup defensive tackle on the depth chart to begin the season, behind Cornelius Griffin, Anthony Montgomery, and Kedric Golston.

[26] On November 23, 2008, Alexander collected a season-high three solo tackles and made his first career sack during a 20–17 win at the Seattle Seahawks in Week 12.

[28] In Week 16, Alexander made one tackle before exiting in the third quarter of the Redskins’ 10–3 victory against the Philadelphia Eagles due to a hamstring injury.

[31] Alexander entered training camp as a backup defensive tackle in 2009 and competed for a roster spot against Antonio Dixon, Kedric Golston, Vaka Manupuna, and Anthony Montgomery.

[33] On December 13, 2009, Alexander collected a season-high three solo tackles and made one sack during the Redskins’ 34–13 win at the Oakland Raiders in Week 14.

[34] Alexander finished the 2009 NFL season with 23 combined tackles (18 solo), two sacks, one pass deflection, and one forced fumble in 16 games and zero starts.

[15] Head coach Mike Shanahan named Alexander the backup outside linebacker, behind starters Andre Carter and Brian Orakpo, to begin the regular season.

[45] Head coach Mike Shanahan named Alexander the backup outside linebacker, behind Ryan Kerrigan and Brian Orakpo, to begin the regular season.

[53] On September 21, 2012, he was fined $15,750 by the NFL for performing a horse collar tackle on wide receiver Danny Amendola during a 31–28 loss at St. Louis Rams in Week 2.

Head coach Bruce Arians named Alexander and Sam Acho the starting outside linebackers to begin the regular season.

[68] On September 23, 2013, the Arizona Cardinals officially placed Alexander on injured reserve after it was discovered he had ruptured the Lisfranc ligament in his right foot.

[70] Head coach Bruce Arians named Alexander the backup inside linebacker, behind Larry Foote and Kevin Minter, to begin the regular season.

[73] Alexander entered training camp slated as a backup outside linebacker and competed for a roster spot against Kareem Martin and Markus Golden.

[76] Head coach Jack Del Rio named Alexander the backup strongside linebacker, behind Ray-Ray Armstrong, to begin the regular season.

[91] In 2018, Alexander played in 16 games with eight starts, finishing fourth on the team with 74 tackles, second with 6.5 sacks, nine passes defensed, and two forced fumbles, and a career-high two interceptions.

So with that tragedy really pushing me to something that I wasn’t quite sure what it was and the modeling of those men that I mentioned, my teammates, my brothers, I soon found out that that was Christ.”[98] When he joined the Redskins in 2006, Alexander gained the nickname "One Man Gang", due to the versatility of football positions he can play: offensive guard, tight end, linebacker, fullback, defensive tackle, defensive end, and special teams.