Fassbender has been developing the project based on Irish myth stories, with writer Ronan Bennett, who has been working on the project since last year.
Michael Fassbender is to take the lead in a new project written by Ronan Bennett, whose credits include Public Enemies and The Hamburg Cell.
Fassbender will star as Cuchulain, the central hero of the Ulster Myth Cycle in the film (one of the four branches of Irish mythology), which has a working title Irish Myths.
Development funding is already in place for the project which is being produced by Finn McCool Films, the London based production company set up by Fassbender and Bennett.
It is not yet known who will direct the project.
Fassbender is currently in Berlin promoting Haywire. He will next be seen in Prometheus for Ridley Scott.