Margot plays Sharon Tate in the film directed by Quentin Tarantino.
The character moves in next door to the main character, Rick Dalton (DiCaprio), just as his career begins to dwindle.
Leo's character is loosely based on Burt Reynolds and Tarantino claims he had DiCaprio in mind when he wrote the script for Once Upon A Time In Hollywood.
According to the Daily Mail, Leo reportedly took a $5 million pay cut upfront, reducing his standard $20 million a movie to $15 million.
"He kind of stands alone today, like Al Pacino or Robert De Niro were in the ’70s, where they weren’t trying to do two movies a year — they could do anything they wanted, and they wanted to do this. So that means this must be pretty good," Tarantino boasted of the actor.
The film is set in 1969 Hollywood, and follows an alternate timeline that combines "multiple storylines in a modern fairy tale tribute to the final moments of Hollywood's golden age."
DiCaprio's character falls into alcoholism after his career begins to plummet, and is accompanied by his best friend and stunt double Cliff Booth (played by Pitt).
Once Upon A Time in Hollywood is Tarantino's ninth film, and will go into wide release on July 26.
