Once Upon a Time in Hollywood takes place in Los Angeles in 1969. The movie follows an aging actor (Leonardo DiCaprio) and his stunt double (Brad Pitt), who encounter real-life Hollywood figures, including Tate.
Robbie worked with a movement coach to convey Tate's lightness and brightness in the new film. She said her training was very different than her work to portray figure skater Tonya Harding in I, Tonya.
"It was such a strange challenge," the star said. "I find it much easier to go dark and angry. With Tonya, I wanted to go really heavy, almost like she had weights on her feet. This time I was trying to do the reverse."
Tate, a model and actress, was 26 and pregnant when she was killed by members of the Manson Family in August 1969. Tarantino said Robbie's name immediately came up when he was casting Tate in the film.
"Margot looks like Sharon Tate... And she can convey Sharon's innocence and purity -- those qualities are integral to the story," the director said.
Once Upon a Time in Hollywood is Tarantino's first film not produced by Harvey Weinstein. It is also his first release since the New York Times interview where Uma Thurman described her car crash on the set of Kill Bill and how Tarantino spit on and choked her in an attempt at authenticity while filming scenes.
"The thought definitely crossed my mind, like, Will people view this decision as conflicting with what I'm doing on the producing side," Robbie said of working with Tarantino.
"I don't know how to say what I feel about it, because I'm so grateful to be in a position of power and to have more creative control when that is embraced and encouraged now," she added, referencing her female-led projects.
"At the same time, I grew up adoring movies that were the result of the previous version of Hollywood, and aspiring to be a part of it, so to have those dreams come true also feels incredibly satisfying," the star said. "I don't know. Maybe I'm having my cake and eating it too."
Once Upon a Time in Hollywood opens in theaters July 26. The film released a trailer featuring DiCaprio and Pitt in May.