English theater and film actress best known for her role as Petunia Dursley in the Harry Potter film franchise. She won the 1997 Drama Desk Award for her one-person performance of T.S. Eliot's "The Waste Land."
She had her breakout stage role as Julia in The Rivals.
She played Marnie Stonebrook on the 2011 season of True Blood.
She was in a committed relationship with actress Saffron Burrows from 2002 until 2011.
She had a supporting role opposite Colin Firth in the 2009 film Dorian Gray.