They join previously announced stars Rosamund Pike, Kate Winslet and Taron Edgerton, who will play Moominmama, Mrs Fillyjonk and Moomintroll, respectively. British stars Richard Ayoade, Matt Berry and Will Self will also star.
Check out some concept art for Moominvalley below.
The series, a reboot of a 1970s stop-motion animation, will follow the adventures of a family of white, hippopotamus-like beings known as Moomins.
Katie Leung (Harry Potter and the Goblet of Fire) and Rebecca Root (The Danish Girl, Boy Meets Girl) also join the cast as characters Too-Ticky and Misabel.
Moominvalley has already been commissioned for two seasons consisting of 13 22-minute-long episodes each, and is slated to debut in spring 2019.