Carter -- who was nominated for an Oscar for "The Wings of the Dove," and most recently starred in "Charlie and the Chocolate Factory" -- will play Bellatrix Lestrange, Sirius Black's cousin and a Death Eater in the fifth movie based on author J.K. Rowling's series of books about a boy wizard.
Warner Bros. also announced that composer Nicholas Hooper -- who won a British Academy of Film and Television Arts award -- will compose the film's score. He is collaborating with British film director David Yates, with whom he has a 15-year history.
Yates directed "The Girl in the Cafe," "Sex Traffic" and "State of Play."
Returning "Potter" cast members include Daniel Radcliffe, Rupert Grint, Emma Watson, Robbie Coltrane, Ralph Fiennes, Michael Gambon, Brendan Gleeson, Jason Isaacs, Gary Oldman, Alan Rickman, Maggie Smith, Emma Thompson, Julie Walters, David Thewlis, Fiona Shaw, Richard Griffiths, David Bradley, Robert Hardy and Mark Williams.
"Harry Potter and the Order of the Phoenix" is scheduled to be released in 2007.