Staunton will follow Claire Foy, who played Elizabeth in Seasons 1 and 2, and Olivia Colman, who portrayed the monarch in Season 3.
Colman will reprise the role in Season 4, which has yet to be released.
"I have loved watching 'The Crown' from the very start. 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," Staunton said in a statement.
"I am genuinely honored to be joining such an exceptional creative team and to be taking The Crown to its conclusion."
Series creator Peter Morgan initially planned six seasons of "The Crown," which follows Elizabeth's reign throughout the decades.
"Now that we have begun work on the stories for S5 it has become clear to me that this is the perfect time and place to stop," Morgan said.
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Morgan confirmed Staunton's casting in a statement Friday.
"I'm absolutely thrilled to confirm Imelda Staunton as Her Majesty the Queen for the fifth and final season, taking 'The Crown' into the 21st century. Imelda is an astonishing talent and will be a fantastic successor to Claire Foy and Olivia Colman," he said.
Staunton is known for her work in theater and was nominated for an Oscar for Best Actress for her title role in "Vera Drake."
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