“I am so excited to be joining the cast and crew of 'The Crown' and to have the opportunity to portray such a complicated and controversial woman,” Anderson said in a statement, which was posted on the show's Twitter account.
“Thatcher was undoubtedly formidable but I am relishing exploring beneath the surface and, dare I say, falling in love with the icon who, whether loved or despised, defined an era.”
Thatcher served as the first female prime minister from 1979 to 1990 and leader of the Conservative Party from 1975 to 1990. She died in April 2013 at the age of 87.
Anderson will join Oscar-winner Olivia Colman who plays Queen Elizabeth II, Helena Bonham Carter who portrays Princess Margaret and Tobias Menzies as Prince Philip in the Emmy award-winning series, which has jumped forward in time and will be set in the late '70s.
It was also announced that Emma Corrin is set to play Lady Diana Spencer in the upcoming fourth season.
"The Crown" will drop on Netflix for its third season on November 17, 2019.