The Hollywood Reporter confirmed Monday Gerwig, 35, and Baumbach, 49, will co-wrote the new Warner Bros. film.
Variety said Warner Bros. had Gerwig and Baumbach in mind since closing a deal with Mattel Films in January to distribute the movie. Gerwig is also being eyed to direct the film.
"Playing with Barbie promotes confidence, curiosity and communication throughout a child's journey to self-discovery," Robbie said in January. "Over the brand's almost 60 years, Barbie has empowered kids to imagine themselves in aspiration roles from a princess to president."
"I'm so honored to take on this role and produce a film that I believe will have a tremendously positive impact on children and audiences worldwide," she added.
Gerwig and Baumbach have collaborated on previous films, including Mistress America and Frances Ha. Gerwig is known for writing and directing Lady Bird, which was nominated for five Academy Awards, including Best Picture, while Baumbach's film The Squid and the Whale was nominated for Best Original Screenplay.