Staunton succeeds Olivia Colman as Queen Elizabeth II in the fifth season, which marks the first season of the show to air since the queen's death on Sept. 8.
"I have loved watching 'The Crown' from the very start," Staunton said in a statement. "As an actor, it was a joy to see how both Claire Foy and Olivia Colman brought something special and unique to Peter Morgan's scripts. I am genuinely honored to be joining such an exceptional creative team and to be taking "The Crown" to its conclusion." Previously, Staunton has played Lady Maud Bagshaw in "Downton Abbey," the title character in the movie "Vera Drake," and Dolores Umbridge in the Harry Potter movies.