Anya Taylor-Joy
Prior to being cast in The Witch as Thomasin, Anya Taylor-Joy was a relative unknown, having appeared in two relatively minor roles prior to the film's release. When Taylor-Joy auditioned for the role, Eggers was impressed by her command of the script, the ease with which she took to Early Modern English, and her ability to embody Thomasin. When he saw Taylor-Joy (her audition tape was the first Eggers saw), he saw Thomasin -- an initially naive and sheltered girl that embraces the devil and joins the witch’s coven. Taylor-Joy is also English, which allowed her to broadly capture the accent her colonist character would have had after emigrating from England to the new world.
Taylor-Joy took a big risk in accepting the role of Thomasin. She had been offered a significant pilot on the Disney Channel, but decided to task a risk, because she "had this really good feeling about The Witch that made [her] willing to forego the Disney experience for the thing that felt unknown to me, the thing that felt sacred.” Her risk paid off, as the role launched Taylor-Joy's career and made her a star.
Ralph Ineson
Ralph Ineson is William, the gruff, headstrong patriarch of the family at the center of the film. Born in Leeds, England, Ineson had appeared in a number of period films before taking a supporting turn in The Witch. Like Taylor-Joy, Ineson was cast because of his background and the ease with which he was able to say his lines in Early Modern English. Ineson's abilities were aided by his background and work performing open-air Shakespeare productions in Lancaster, England.
During filming, Eggers asked Ineson to step in and direct young Harvey Scrimshaw, who played the minor role of Caleb. Eggers didn't have children at the time, but Ineson did, so he felt that Scrimshaw could better understand direction from a man who was used to speaking with children. Ineson obliged.
Kate Dickie
The English actress Katie Dickie plays Katherine, William's grieving wife and matriarch of the family. Dickie has had a long and storied career in film, stage, and television. She said she first became interested in appearing in The Witch after reading writer/director Robert Eggers' script. In an interview after the release of the film, she said she "loved the authenticity" of it and the way it allowed viewers to see what life was like for people who lived in the early 17th century. Likewise, she felt the party was meaty because of the shifting family dynamics at play. Still, the role was physically challenging, as they worked near an abandoned logging town in Canada with limited resources.
Ralph Ineson was cast before Dickie, making it easier for Eggers to see the dynamic between the two actors and envisage Dickie as Katherine. Growing up in Scotland, she was intimately familiar with tales of witches and magic -- especially the Grimm fairy tales, which she favorably compared The Witch to.
