The Netflix royal drama is set to return for two more series with Imelda Staunton starring as the Queen, Jonathan Pryce taking over the role of Prince Philip and Lesley Manville cast as Princess Margaret.
Trainspotting star Miller, 48, has been announced to take on the role of Conservative PM in the fifth series.
Sir John Major served as PM from 1990 to 1997. He was succeeded by Labour leader Tony Blair in May 1997 but was made a 'special guardian' of Princes William and Harry after their mother Princess Diana's death in August that year. He was a guest at the wedding of Prince Harry to Meghan Markle in 2019.
Read more: Jonathan Pryce confirmed for The Crown
Miller rose to fame after starring in Danny Boyle's 1996 film Trainspotting and has gone on to have a successful career in film, television and on stage.
He starred as Sherlock Holmes in the US TV drama Elementary between 2012 and 2019, and in 2012 shared the Olivier Award for Best Actor with Benedict Cumberbatch for their performance in Frankenstein at the National Theatre.
It was previously announced that Princess Diana will be played by Australian actress Elizabeth Debicki for seasons five and six of The Crown.
She will take over from Emma Corrin, who played the younger Diana Spencer in season four of the show.
The series extending to a sixth season was confirmed by the show's creator Peter Morgan in July last year.
He said: “As we started to discuss the storylines for [Season 5], it soon became clear that in order to do justice to the richness and complexity of the story, we should go back to the original plan and do six seasons.
“To be clear, [Season 6] will not bring us any closer to present day — it will simply enable us to cover the same period in greater detail.”
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