Babylon follows multiple characters as they experience the decadence and debauchery of early Hollywood.
"Babylon is about a group of people who find themselves in early Hollywood at a time of extreme depravity and debauchery and excess," Chazelle said. "It's the biggest thing I've ever tried to do."
"It was such an insane time," Robbie added. "It's just wild, like the Wild West."
Pitt plays Jack Conrad, "the biggest film actor at the top of his game," while Robbie portrays Nellie LaRoy, an aspiring actress.
"They have an ambition to be part of something bigger than themselves," Pitt said of the characters.
Babylon opens in theaters Dec. 23.
Chazelle is known for the films Whiplash, La La Land and First Man.