He received an invitation to the NFL Combine and completed all the required drills except for the three-cone and bench press due to a shoulder and calf injury.

On March 20, 2013, he participated at Tennessee's pro day and performed the broad jump, three-cone drill, and vertical for scouts and representatives.

[15] Representatives from all 32 NFL teams attended including the Pittsburgh Steeler's head coach Mike Tomlin and offensive coordinator Todd Haley to scout Justin Hunter, Cordarrelle Patterson, Tyler Bray, and eight other prospects.

[21][22] Hunter entered the regular season as the Tennessee Titan's fourth wide receiver on their depth chart, behind veterans Kenny Britt, Nate Washington, and Kendall Wright.

[23] On September 22, 2013, he recorded his first career NFL reception on a 34-yard touchdown pass from Jake Locker that was the game-winning score in a 20–17 win over San Diego Chargers.

[28][29] Hunter entered training camp in 2014 competing with Marc Mariani and Dexter McCluster to be the Tennessee Titan's third wide receiver on their depth chart.

Head coach Ken Whisenhunt named him the third wide receiver to begin the regular season, behind Kendall Wright and Nate Washington.

[35][36] Throughout training camp in 2015, Hunter faced stiff competition for the vacant starting wide receiver position left by Nate Washington.

He lost the job to veteran Harry Douglas and was named the third wide receiver on the depth chart ahead of Hakeem Nicks, Jacoby Ford, and rookie Dorial Green-Beckham.

[39] The following week, he caught a season-high four passes for 47 receiving yards, but had to leave after suffering an apparent ankle injury during a 27–10 loss to the Carolina Panthers.

[40] On Monday, November 16, 2015, Hunter was added to the season-ending injury reserve list after having surgery the day before to repair a fractured ankle suffered previous game against the Panthers.

[41][42] After returning from a fractured ankle, Hunter entered training camp competing to be the Titans third option at wide receiver with Dorial Green-Beckham and Andre Johnson.

[47] Rex Ryan named him the team's fifth wide receiver on their depth chart behind Robert Woods, Marquise Goodwin, Greg Salas, and Walter Powell.

Hunter made his Buffalo Bills debut on October 9, 2016, against the Los Angeles Rams and caught a four-yard touchdown pass from Tyrod Taylor.

[21][52] Hunter entered Steelers training camp competing for a backup wide receiver position against Sammie Coates, JuJu Smith-Schuster, Cobi Hamilton, Demarcus Ayers, Eli Rogers, and Darrius Heyward-Bey.

He was named the sixth wide receiver to begin the regular season, behind Antonio Brown, Martavis Bryant, Heyward-Bey, Smith-Schuster, and Rogers.

[54] On October 1, 2017, in Week 4, Hunter made his official Steelers regular season debut and finished a 26–9 victory over the Baltimore Ravens with one reception for five yards.

[55] On December 25, 2017, Hunter caught his first touchdown as a member of the Steelers on a five-yard pass by quarterback Ben Roethlisberger in their 34–6 win against the Houston Texans.