The 'Night Manager' star will take over the lead for the show's third and fourth seasons.
The second season is set to debut on December 8 on Netflix. Seasons 3 and 4 have not been officially ordered, but early production is said to be underway.
Last year, series creator Peter Morgan said that he intended to replace key cast members in later seasons, to better portray the main characters as they age.
The series tells the inside story of Queen Elizabeth II's reign, as the fragile social order established after the Second World War breaks apart.
Each season follows roughly a decade in the life of the Queen, and producers planned from the outset to recast their lead roles after season 2. The new season is expected to roughly cover from 1957 to 1964.
The second season of 'The Crown' is set to debut this december on the streaming service.