Melvin was an undrafted free agent who first signed with the Tampa Bay Buccaneers in 2013. He was released by the Bucs the following year, and from October of 2014 until September of 2016 Melvin bounced around various rosters and practice squads.
Melvin played in 12 games total during that span suiting up for the Baltimore Ravens, Miami Dolphins and New England Patriots. He started 2 games and recorded 24 total tackles.
The Colts signed Melvin after he was released by the Dolphins in September last year. Since that time, Melvin has started 18 of a possible 24 games recording 82 tackles and 19 passes defended.