The La Vie En Rose star is set to appear in The Dark Knight Rises, which is being helmed by Inception director Christopher Nolan, alongside Christian Bale, who returns as the caped crusader, and Hathaway as Selina Kyle/Catwoman.
It is not yet known whether the 35-year-old will play a romantic interest or a rival superhero to Anne's Catwoman character.
According to the Le Parisien newspaper, the addition of Cotillard comes as a surprise.
Marion, who is expecting a baby in April with her partner Guillaume Canet, is said to have signed on to the Batman project on Saturday in Paris.
Filming for The Dark Knight Rises is set to begin soon and it should be released in June 2012.