"Green Book", which chronicles the relationship between African-American classical pianist Don Shirley and his white driver, is the critics pick for the film of the year, while Mortensen has been named Best Actor.
Bradley Cooper has picked up the Best Director for his filmmaking debut, "A Star Is Born", while his leading lady, Lady GaGa, has been named Best Actress and their co-star Sam Elliott Best Supporting Actor.
As well as "Green Book", the National Board of Review's top films of 2018 are "The Ballad of Buster Scruggs", "Black Panther", "Can You Ever Forgive Me?", "Eighth Grade", "First Reformed", "If Beale Street Could Talk", "Mary Poppins Returns", "A Quiet Place", "Roma", and "A Star Is Born".
The National Board of Review honorees will be feted at a gala in January, 2019 at Cipriani 42nd Street in New York.
The full list of winners is: