Christina Hodson will pen the screenplay for the forthcoming film, which will see the 26-year-old actress reprise her 'Suicide Squad' role as the sexy, psychotic supervillain, and produce the motion picture.
According to The Wrap, Warner Bros. are yet to officially comment about the project, which will feature several female superheroes rather than just be based purely on Quinn.
But it's not yet clear how each character, and which ones, will feature in the movie.
Hodson has written three scripts which have made the Black List - an annual survey of the most liked movie screenplays yet to be released - including a 'Fugitive' reboot and 'The Eden Project', which was sold to Sony and Material Pictures.
She recently penned 2016 thriller 'Shut In', which stars Naomi Watts as psychologist Mary Portman who starts believing there is someone inside her house after a storm breaks out.
In September, Robbie was reported to have signed a "first-look" deal with Warner Bros. to produce the Quinn spin-off film.
She is said to have fallen in love with the character after portraying her in 'Suicide Squad'.
It's not known whether Quinn's dangerous lover The Joker (Jared Leto) will star in the spin-off or Batman (Ben Affleck), who is traditionally the superhero trying to stop the pair's criminal plans.
But Robbie has previously admitted she would love Quinn and The Joker to reunite.
She said: "I'm trying to make that happen. Not for anything specifically, but just something - there's so much more to do."