General manager Jim Hendry told reporters, including the Chicago Tribune's Paul Sullivan, that Lopez will be used as a "swing man."
"We've been scouring, looking for people like this," Hendry said. "He's had a really good year in Triple-A with the Braves.... With our injury situation and even some setbacks at the Triple-A level, we felt like it was a good move."
Lopez, 35, has started 199 big league games and appeared as a reliever in 28 more, going 75-82 with a 4.85 ERA. He started 33 games with Arizona last season, going 7-16 with a 5.00 ERA.
The Braves signed him as a minor-league free agent before the season, and he's gone 6-1 with a 2.59 ERA in nine starts for Triple-A Gwinnett. He will be added to the team's 40-man roster on Friday and is expected to join the team Friday before its game with the Pirates.
The Braves received Double-A left-hander Ryan Buchter in exchange for Lopez. Buchter, 24, has a 3.38 ERA in 16 relief appearances at Class A and Double-A, recording 30 strikeouts in 21 1/3 innings. Buchter has 251 strikeouts and 141 walks in 212 professional innings.