The X-Men actress joins Jeremy Renner and Gemma Arterton in the supernatural thriller from Paramount Pictures, reports The Playlist.
It is not yet known what role Janssen will portray in the film.
Renner and Arterton are playing the titular characters based on the classic fairytale. In the movie, Hansel and Gretel grow up to become witch hunters.
Director Tommy Wirkola (Dead Snow) will begin filming the project on March 7.
Adam McKay and Will Ferrell are producing.