Miriam Margolyes has made over 40 major film appearances in such diverse roles as Professor Sprout in Harry Potter and the Chamber of Secrets; Nurse in Baz Luhrmann's Romeo + Juliet, with Leonardo DiCaprio and Claire Danes; Mrs. Mingott in Martin Scorsese's The Age of Innocence, for which she won the BAFTA Award for Best Supporting Actress; Peg Sellers in The Life and Death of Peter Sellers, with Geoffrey Rush; Dolly de Vries in Being Julia, with Annette Bening; Dorcas, the housekeeper in Ladies in Lavender, with Judi Dench and Maggie Smith; and Flora Finching in Little Dorrit.

Happy Feet marks Margolyes' third project with George Miller, having voiced the character of Fly, the female border collie, in the award-winning feature Babe and its sequel, Babe: Pig in the City. Her voice has also been heard as the famous Cadbury's Caramel Rabbit, the Glowworm in James and the Giant Peach, and the Matchmaker in Mulan.