He was signed by the Miami Dolphins as an undrafted free agent in 2012 and also played for the Baltimore Ravens and New England Patriots.

[1][2] He helped lead Detroit Country Day to an 11–3 record as a senior and an appearance in the state championship.

He rushed for 305 yards on 29 carries and scored four touchdowns in the state semifinal to lead the Yellow Jackets to a 37–30 victory.

He played sparingly his first three seasons, primarily as a back-up to Armando Allen, Robert Hughes and Cierre Wood.

On October 16, 2014, Gray was signed to the active roster before their Thursday Night Football game against the New York Jets.

On November 16, 2014, Gray rushed for 201 yards, and a franchise-record four touchdowns on 37 carries in his fourth NFL game, leading the New England Patriots to a 42–20 victory over the host Indianapolis Colts.

[12] He would only record 91 more total yards in the season, and was inactive for four of the Patriots remaining nine games, including the team's win in Super Bowl XLIX.

[17] Gray was signed off the Dolphins' practice squad to the Jacksonville Jaguars active roster on December 15, 2015.