Kimbrel, who also was selected as the NL's top rookie for June, converted all 10 of his save opportunities in the just-completed month, allowing six hits and no runs in 12 2/3 innings over 13 appearances.
The 23-year-old also continued to increase his MLB-best scoreless streak to 36 2/3 innings, and set a new rookie mark for saves in one season when he locked up a 3-1 victory over the Washington Nationals. In that game, Kimbrel recorded his 41st save, snapping the record set last season by Neftali Feliz of Texas.
This marks the third straight month that a Braves player has taken the monthly honor, with first baseman Freddie Freeman the July winner. It's the first time that has occurred in the NL and fourth time overall.
On the season, the Huntsville, Alabama native is 4-2 with a 1.57 earned run average over 70 games.
Other rookies receiving votes included Astros outfielder J.D. Martinez, Mets outfielder Lucas Duda, Arizona first baseman Paul Goldschmidt, Atlanta starter Brandon Beachy, Padres first baseman Jesus Guzman and pitcher Cory Luebke, and Reds outfielder Yonder Alonso.