Variety reports that the Atonement star will join Ralph Fiennes and Jude Law in the period drama.
Bill Murray and Jason Schwartzman will also re-team with Anderson on The Grand Budapest Hotel, which is set in the early 20th century at a hotel in Hungary, and follows the trials and tribulations of its concierge Mr Gustave.
Ronan will next be seen in Kevin McDonald's drama How I Live Now, and she will star as Mary Queen of Scots in a new biopic.
She will also appear in In Time helmer Andrew Niccol's sci-fi thriller The Host, which is adapted from a novel by Twilight author Stephenie Meyer.
Watch Saoirse Ronan discussing her role in The Host with Digital Spy below: