"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 tweet. "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, who died in 2013, was Great Britain's first female prime minister and served from from 1979 to 1990. She was called the Iron Lady for her political and personal toughness.
The fourth season of "The Crown" is in production.
Season 3 of the drama series returns on November 17. Academy Award-winner Olivia Colman takes over the role of Queen Elizabeth II from Claire Foy, who played the character for the drama's first two seasons.
- Gillian Anderson will play Margaret Thatcher in 'The Crown' Season 4
- Former British PM Margaret Thatcher refused to fly with a panda
- 'American Idol' crowns new winner
- 'Survivor' Season 37 crowns winner
- Danube escape: Budapest's Margaret Island
- 'The Voice' season 15 winner crowned
- 'This Is Us' season three finale reveals the identity of 'her'
- 'It's Pele' -- Arsene Wenger recalls seeing Kylian Mbappe play for first time
- A high school's 'Alien' play is the talk of Hollywood
- Milo Ventimiglia says he was told he's too old to play 'Batman'