The Crown will end with its fifth series, which will see Imelda Staunton play the Queen.
“I could not be happier to be playing Princess Margaret,” Oscar-nominee Manville said in a statement confirming her signing on Twitter.
“The baton is being passed on from two formidable actresses and I really don’t want to let the side down.
“Furthermore, to play siblings with my dear friend Imelda Staunton will be nothing short of a complete joy,” the Mum actress said.
The fourth series of the drama, featuring Gillian Anderson as Margaret Thatcher and Olivia Colman returning as the Queen, is expected to air later this year.
Lesley Manville joins The Crown: ‘I could not be happier’