Braun was tied for second in the league in homers and RBIs, while ranking seventh in slugging percentage (.620) and runs scored (17). His 33 hits was tied for ninth in the NL in the month.
Braun was clutch at the plate throughout the month as the Brewers locked up home-field advantage in the NL Division Series, beginning with an 11th-inning walk-off homer against the Rockies on Sept. 13.
On Friday, he hit a go-ahead three-run homer in the eighth inning to lead the Brewers to a 4-1 division-clinching win over the Marlins.
By the end of the regular season, Braun had become just the second player in Brewers franchise history to produce a 30-homer, 30-steal season (Tommy Harper had 31 homers and 38 stolen bases in 1970). He also finished the year with a league-leading .597 slugging percentage.
His other end-of-the-season totals included a .332 batting average (second in the NL), 109 runs scored and 111 RBIs.
This is Braun's fourth career monthly award, and his second this season, having previously earned the honor in July 2007 and '08, as well as April of this year.
Braun's teammate Prince Fielder also received recognition for a September in which he hit .329 with nine homers, 18 RBIs, 14 runs and a .706 slugging percentage.