The six-part drama, which was announced in January, is based on the memoirs of Jennifer Worth and focuses on midwives working in 1950s London.
Worth was working on the project with screenwriter Heidi Thomas, who previously penned Upstairs Downstairs and Cranford, but passed away earlier this month.
Newcomer Jessica Raine has now landed the lead role of Jenny, who goes to live with a group of nuns and nurses. Raine has previously appeared in two episodes of Garrow's Law and the movie Robin Hood.
Agutter and Hart will both play members of Jenny's new community, along with Pam Ferris, Judy Parfitt, Helen George and Bryony Hannah.
The BBC's controller of drama commissioning Ben Stephenson said: "This superb cast of some of our best established and new actresses will bring to life the extraordinary true stories and friendships of midwifery and family in 1950s East End London."
Meanwhile, the show's executive producer Pippa Harris described the series as "a fascinating portrayal of birth, life, death and a community on the bring of huge social change".
Filming for Call The Midwife will begin in London shortly and the drama will air on BBC One next year.
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