Medlen also earned the honor in August, making him the first hurler to net consecutive monthly honors since Ubaldo Jimenez did so in April-May 2010 while with the Rockies.
Medlen also is the first Braves pitcher to win back-to-back monthly awards since Greg Maddux accomplished the feat in June-July 2001.
Medlen went undefeated for the second consecutive month, going 4-0 and striking out a Major League-high 46 batters in September. His 1.26 ERA also ranked fourth among pitchers with at least 26 innings, and opposing hitters batted only .169 against him.
The Braves won all six of Medlen's September starts, as the right-hander improved to 9-0 as a starter this season.
According to the Elias Sports Bureau, the only other Major Leaguers to go at least 9-0 as a starter were Tom Zachary (1929 Yankees), Whitey Ford (1950 Yankees) and Ken Holtzman (1967 Cubs).
Atlanta's Mike Minor and Craig Kimbrel were also considered for the award. Minor went 4-0 with an 0.87 ERA, while Kimbrel went 3-0 with 10 saves and 25 strikeouts in 12 2/3 innings.