Christian Coulson starred in Love in a Cold Climate
Christian Coulson, 23, will be known to millions of fans around the world as Tom Riddle, a younger incarnation of Harry Potter's enemy Lord Voldemort, in Harry Potter and the Chamber of Secrets.
Black Hawk Down actor Jason Isaacs has also been added to the cast as Lucius Malfoy, Draco's dad, while comedian Mark Williams will play Ron's father Arthur Weasley.
Harry Potter and the Chamber of Secrets, due in cinemas in November, is expected to match the popularity of the first Harry Potter movie, which has become the second most successful film in history.
Coulson's biggest role before Tom Riddle was as the adventurous Matt Radlett in 1930s-set BBC television series Love in a Cold Climate.
He has also filmed parts in the new Nicole Kidman drama The Hours and the latest film from Elizabeth director Shekhar Kapur, Four Feathers.
Coulson, who was a member of the UK's National Youth Music Theatre, will become recognisable to a legion of film fans as the former Hogwarts pupil whose desire for power turns him into Harry Potter's enemy.
Jason Isaacs will play another bad guy, the vicious Lucius Malfoy. Isaacs is best-known for roles in war films including Black Hawk Down, The Patriot and new Nic Cage Second World War movie Windtalkers.
Comedy fans will recognise Mark Williams as one of the team in UK TV hit The Fast Show.
He has also appeared in big screen children's adventures 101 Dalmatians and The Borrowers.
Comic favourite Miriam Margolyes, star of Cats and Dogs and William Shakespeare's Romeo and Juliet, will play Professor Sprout.
It was already been known that Kenneth Branagh would play Professor Gilderoy Lockhart.
It has been reported that filming has recently been taking place for Harry Potter and the Chamber of Secrets at the historic Glenfinnan Tower in Scotland.