Brad Pitt has come on board to star in Steve McQueen’s “Twelve Years a Slave” with River Road producing and financing.Deal for Bill Pohlad’s River Road to join “Slave” closed Monday. Summit will handle international sales at the American Film Market. Michael Fassbender, who toplined McQueen’s “Shame,” signed on for “Twelve Years a Slave” two weeks ago. McQueen will direct from a script he co-wrote with John Ridley. Chiwetel Ejiofor and Pitt will also star in the true story of Solomon Northup, a New York citizen who was kidnapped in Washington in 1841 and rescued from a cotton plantation in Louisiana in 1853. Pitt is also producing through Plan B with Plan B partners Dede Gardner and Jeremy Kleiner along with Pohlad and the film is expected to start production early next year. CAA is arranging financing for the pic and representing U.S. rights.