The deal is for four years, $21 million, a source told NFL Media's Jeff Darlington.
Shelby adds a proven stout run defender to the Falcons defensive line and an improving pass rusher. Shelby compiled 31 quarterback hurries, 3.5 sacks and four passes defensed in 2015.
As Around The NFL's Chris Wesseling noted, Shelby's exceptionally strong hands allow him to bulrush offensive lineman, disrupting the quarterback's pocket and discombobulating the run game.
An ascending talent, Shelby is a significant addition to Dan Quinn's defense. Atlanta needs him to grow as a pass rusher, but he's an immediate upgrade on a defensive front in need of a talent infusion opposite Vic Beasley.