Wearing a black turtleneck and white mini-skirt and boots, she stands outside a Hollywood cinema.
Margot added the simple caption: "Hollywood. 1969. #OnceUponATimeinHollywood."
Pregnant Tate was murdered by members of Charles Manson's The Family cult and her attack provides the backdrop to Tarantino's much-anticipated new film, which hits cinemas in July.
Margot's fellow Australian, Damon Herriman, will play Manson in the film, which centres upon the relationship between a TV actor and his longtime stunt double as they try to find success in the Los Angeles film industry in 1969. DiCaprio's actor just happens to live next door to the doomed Tate.
Meanwhile, Sharon Tate's sister, Debra, has given the new film her backing after meeting with Tarantino.
She feared the filmmaker's new movie would be "tacky and exploitative" and made it clear she wasn't thrilled by news of the director's decision to cast Australian Robbie as the pregnant Sharon, but she told TMZ last year (2018) that Quentin reached out to her to address her concerns about the movie, and now she's supporting the project.
"This movie is not what people would expect it to be when you combine the Tarantino and Manson names," she tells the outlet.
The filmmaker has always made it clear that "Once Upon a Time in Hollywood won't be about the Manson Family murders in 1969, but the slayings will feature in the period film.