Gattis had been sidelined since June 29 with a bulging disk in his lower back.
The return of Gattis adds an important bat to the middle of the Braves' lineup. Gattis is hitting .290 with 16 homers -- one behind Justin Upton's team-leading 17 -- and 39 RBIs.
The Braves optioned catcher Christian Bethancourt to Triple-A Gwinnett.
Upton is also in Monday night's lineup after he left Sunday's game against the Phillies with triceps tightness after being hit by a pitch.