Zoo officials say Lun Lun gave birth to the cub at 5:39 a.m. on Wednesday in a specially prepared birthing den.
Zoo Atlanta is one of only four U.S. zoos with the endangered animals. The others are in San Diego, Memphis and Washington, D.C.
Lun Lun was inseminated with sperm from her partner, Yang Yang, in June after the two failed to mate. The couple's previous cubs were Mei Lan, born in 2006, and Xi Lan, born in 2008.
Researchers estimate only 1,600 to 3,000 of the endangered species remain in the wild and another 200 in captivity.