He played college football at University of North Texas and was signed by the Dallas Cowboys as an undrafted free agent in 2012.

He initially attended De La Salle High School (New Orleans, Louisiana) where he played running back and safety, but transferred after his family settled in Haltom City, Texas.

[9] During the final game of the season, against Kansas State University, he set a career-high for rushing yards, with 270.

[16] After being passed over in the 2012 NFL draft because of size concerns, he was signed as an undrafted free agent by the Dallas Cowboys on April 28, 2012.

He was fighting for the third-string running back position with rookie Joseph Randle, when he had a breakout game against the Oakland Raiders, registering 82 rushing yards (6.8 average), but also suffering a season-ending knee injury.

[20] In 2014, he did not see much playing time behind Offensive Player of the Year DeMarco Murray and also fell to third-string behind Joseph Randle.

[21] In 2015, after the team lost Murray to the Philadelphia Eagles in free agency and Dez Bryant to injury in the season opener against the New York Giants, Dunbar earned a more prominent role in the offense.

[23] He entered the fourth game of the season against the New Orleans Saints as the team's leading receiver and recorded a 45-yard run, before tearing the ACL, the MCL and the patellar tendon in his left knee, during a kickoff return, which was a task he was assigned to replace the recently departed Dwayne Harris.

[25] He began training camp on the physically unable to perform list, while recovering from his previous knee injury.

[26] His injury knee flared up and was declared inactive against the Chicago Bears, Green Bay Packers, and Philadelphia Eagles.

[27] On March 16, 2017, Dunbar signed a one-year contract with the Los Angeles Rams, who were looking to replace Benny Cunningham.