Staunton will take over from Olivia Colman, who is portraying the monarch in the third and fourth seasons.
It was initially thought that the royal drama would run for six series, spanning six decades.
The show’s creator Peter Morgan said the show will end in the 21st Century, meaning it will cover the aftermath of the death of Diana, Princess of Wales.
But it’s not likely to extend to more recent events, such as the marriage of the Duke and Duchess of Sussex.
Netflix revealed last week that a total of 73 million households worldwide have watched the show since it began in 2016.
But it failed to make the streaming giant’s UK’s top 10 list of its most popular releases of 2019.
Morgan said: “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.”
‘Special and unique’
In early January, Colman won the best actress award at the Golden Globes for her leading part in series three, which explored storylines including the romance between Prince Charles and Camilla.
Staunton, who starred in Vera Drake and the Harry Potter film series and previously portrayed the Queen in the 2003 TV series Cambridge Spies, said she was already a big fan.
“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,” she said.
The fourth series is currently in production and will see the introduction of Diana, Princess of Wales, played by Emma Corrin, and Margaret Thatcher, played by Gillian Anderson.