Amelia Bones, the Head of the Magical Law Enforcement Office, will be played by Sian Thomas.
She's appeared in several productions for the Royal Shakespeare Company, as well as roles in TV and film.
And the Dursleys will definitely be back in The Order of the Phoenix, after their absence from Goblet of Fire.
Other casting includes Charles Hughes as Young Wormtail and Susie Shinner as Young Lily Potter. CBBC Newsround reported last week that Robbie Jarvis, 19, will play Young James Potter.
Auror Dawlish will be played by Richard Leaf, and Nick Shim has been cast as Zacharias Smith. Gary Oldman is currently in negotioations to return as Sirius Black.