Carter would take over the role played in the first two seasons by Vanessa Kirby.
The second season premiered December 8 on Netflix. In it, Margaret married Antony Armstrong-Jones, the Earl of Snowdon (Matthew Goode) and the season ended with her pregnant with one of their children.
The Crown, created by Peter Morgan, tells the inside story of Queen Elizabeth II’s early reign as the fragile social order established after WWII breaks apart.
It was announced earlier that Olivia Colman would be replacing Claire Foy as Queen Elizabeth in the upcoming third and fourth seasons, which have not yet been ordered but are expected. Morgan previously said he intended to replace key cast members in later seasons, to better portray the characters as they aged.
Carter, star of Sweeney Todd: The Demon of Fleet Street and Alice in Wonderland among others, will next be seen in Warner Bros’ Ocean’s 8, the female-driven caper spinoff directed by Gary Ross. She’s also the voice of Margaret Conroy in Fun Academy Motion Pictures’ first animated family film Sgt. Stubby: An American Hero.