Simmons hit .333 (30-for-90) with six doubles, three home runs and 14 RBIs during the month, leading NL rookies in hits, on-base percentage and batting average.
Making his Major League debut on June 2, Simmons hit safely in 17 of his first 25 contests and led the club with 10 multi-hit games during the month.
The Curacao, Venezuela, native waited until the last day of the month Saturday to have his best offense performance. He went 3-for-4 with an RBI and a run scored in a 7-5 win over the Nationals.
"The way I look at it is, what he does defensively is unbelievable and anything he brings offensively is a bonus," Braves catcher Brian McCann said. "The guy happens to be hitting with guys in scoring position, seems to be getting the big hit, hitting .330. He's doing everything. He's mature, he expects to be here, he expects to produce at a high level. He's a big-time athlete. I don't think there's much he can't do."
The award also marked the fifth consecutive season that a Braves player has won rookie honors.
Simmons was a second-round pick by Atlanta in the 2010 First-Year Player Draft.
Quinn Roberts is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.