The final two seasons of The Crown are set in the 1990s, and the show will conclude in the early 2000s.
Known for her roles as Dolores Umbridge in the Harry Potter franchise and Vera Drake.
"I think my sort of extra challenge, as if I needed it, is that I'm now doing the Queen that we're a little more familiar with," Staunton said in an interview in January for the BBC Woman's Hour.
Staunton joins several big names in the new era of The Crown.
Lesley Manville is joining series five as Princess Margaret, a role previously played by Helena Bonham Carter and Vanessa Kirby.
Jonathan Pryce will portray Prince Philip, taking over from Tobias Menzies.
The upcoming season will cover Princess Diana's split with Prince Charles, the Duke of York's marriage to Sarah Ferguson, and Diana's death. Emma Corrin won the hearts of The Crown fans in the last season when she played the young Princess of Wales, and Australian actress Elizabeth Debicki will play her in the final two seasons.
"Princess Diana's spirit, her words and her actions live in the hearts of so many," Debicki said in a statement when it was announced she had landed the role.
"It is my true privilege and honour to be joining this masterful series, which has had me absolutely hooked from episode one."
Filming for the show began in July so The Crown fans will have to wait until 2022 for the new season.