The Braves gave Hamels, a four-time All-Star selection, a one-year contract worth $18 million, according to the team. After the move, the club has 38 players on its 40-man roster.
Hamels joins a Braves rotation that consists of Mike Soroka, Max Fried and Mike Foltynewicz. Right-hander Julio Teheran and left-hander Dallas Keuchel, the two other members of the team's 2019 starting rotation, are free agents.
Hamels had a 7-7 record with a 3.81 ERA and 143 strikeouts over 27 starts for the Cubs last season. The 35-year-old left-hander posted a 2.98 ERA in 17 starts before straining his left oblique at the end of June.
In 10 starts for Chicago after returning from the injured list, Hamels compiled a 5.79 ERA and allowed opponents to produce a .397 on-base percentage and a .506 slugging percentage.
Hamels is 163-121 with a 3.42 ERA and 2,558 strikeouts in his MLB career, ranking seventh among active pitchers in wins. He was named MVP in the 2008 World Series and NL Championship Series with the Phillies.
The Braves have remained active in the off-season after signing reliever Will Smith and catcher Travis d'Arnaud to multiyear deals. The team also reached agreements with Chris Martin, Darren O'Day, Nick Markakis and Tyler Flowers.