In return, the Cubs received right-handed pitchers Jaye Chapman and Arodys Vizcaino.
The Braves -- who currently hold one of the two National League wild-card spots -- will use the 30-year Maholm to bolster their starting pitching staff. The left-hander is 9-6 with a 3.74 ERA in 21 appearances (20 starts) with the Cubs this season after signing a one-year deal with Chicago in January.
Johnson, a 35-year-old veteran, is averaging .302 with three home runs and 16 RBI over 76 games.
Vizcaino, 21, is out while recovering from elbow ligament replacement surgery. Chapman, 25, has seven saves in 40 relief appearances for Class AAA Gwinnett this season.