Daniel Radcliffe as Harry Potter, who is now entering his sixth year at Hogwarts, with the wizarding world at war.
Rupert Grint as Ron Weasley, Harry's best friend. He develops a relationship with Lavender Brown and later with Hermione Granger.
Emma Watson as Hermione Granger, Harry's other best friend. Watson considered not returning for the sixth film, but eventually decided that "the pluses outweighed the minuses" and could not bear to see anyone else play Hermione.
Michael Gambon as Albus Dumbledore. The legendary wizard and headmaster of Hogwarts. The revelation of Dumbledore's sexuality prompted Gambon to "camp up" around the set when off camera, but his on-screen performance is expected to remain unchanged from the previous films.
Jim Broadbent as Horace Slughorn, the newly appointed Hogwarts Potions master. Broadbent described his costumes as "tweedy", and his character as "comic", while Radcliffe noted that "Slughorn's tragedy will outweigh the comedy".
Alan Rickman as Severus Snape, the former Potions master, who finally achieves his goal of becoming Defence Against the Dark Arts teacher.
Tom Felton as Draco Malfoy, a classmate of Harry, who Harry suspects of carrying out a task for Voldemort across the year, and son of Narcissa Malfoy and nephew to Bellatrix Lestrange.
Bonnie Wright as Ginny Weasley, Ron's younger sister in her fifth year, for whom Harry develops intense romantic feelings. Her feelings for Harry never changed and they finally become a couple right after the final Quidditch match, or in the film when they hide Harry's Potions book by sharing their very first kiss.
Evanna Lynch as Luna Lovegood, a friend of Harry, Ron, Hermione, Neville, and Ginny. Takes Nymphadora Tonks's place in rescuing Harry on the Hogwarts Express.
Robbie Coltrane as Rubeus Hagrid, the Hogwarts gamekeeper and Care of Magical Creatures teacher.
Maggie Smith as Minerva McGonagall, the Hogwarts Transfiguration teacher, deputy headmistress and head of Gryffindor.
David Thewlis as Remus Lupin, is a werewolf, a member of the Order of the Phoenix and former Defence Against the Dark Arts teacher.
Natalia Tena as Nymphadora Tonks, a member of the Order of the Phoenix and an Auror who is in a relationship with Remus Lupin.
Helen McCrory as Narcissa Malfoy, Draco's mother and younger sister of Bellatrix Lestrange. McCrory was originally cast as Bellatrix Lestrange in Order of the Phoenix, but had to drop out due to pregnancy. Naomi Watts was previously reported as having accepted the role, only for it to be denied by her agency.
Helena Bonham Carter as Bellatrix Lestrange, one of Voldemort's principal Death Eaters, older sister of Narcissa, aunt to Draco and Nymphadora, cousin of Sirius Black.
Timothy Spall as Peter Pettigrew, one of Voldemort's principal Death Eaters and former friend of James Potter, Sirius Black and Remus Lupin. Severus Snape's servant.
Mark Williams and Julie Walters as Arthur and Molly Weasley, Ron and Ginny's parents.
James and Oliver Phelps and as Fred and George Weasley, Ron's older twin brothers who love to break rules and play pranks on other people.
Jessie Cave as Lavender Brown, Ron's girlfriend. Watson described her as "perfect for the role," although Cave did not attend the open auditions. An open casting call was held for the part on 1 July, 2007. Over 7,000 girls turned out for the audition and read from a scene with Madam Pomfrey, Hermione, and Ron. Yates tested Grint with the top five choices for Lavender, reading certain lines and kissing, to see which pairing had the best chemistry.
Hero Fiennes-Tiffin and Frank Dillane each play Tom Marvolo Riddle, the child who becomes Lord Voldemort, at age eleven and as a teenager respectively. Fiennes-Tiffin is the eleven-year-old nephew of Ralph Fiennes, who plays the adult Voldemort in the fourth and fifth films. An open casting call was held for the part in July 2007, with applicants reading from a scene involving Riddle trying to persuade Horace Slughorn to explain what Horcruxes are. Christian Coulson, who played Riddle in Chamber of Secrets, expressed an interest in returning. However, Yates responded that since Coulson was nearly 30, he was too old for the part.
Gemma Jones as Poppy Pomfrey, the school nurse.
Warwick Davis as Filius Flitwick, the Charms professor and head of Ravenclaw.
David Bradley as Argus Filch, the school caretaker.
Georgina Leonidas as Katie Bell, the Gryffindor Chaser who is injured by a cursed necklace.
Anna Shaffer as Romilda Vane, a student obsessed with Harry; she tries to make him fall in love with her by using love potions.
Scarlett Byrne as Pansy Parkinson, a Slytherin girl in Harry's year.
Matthew Lewis as Neville Longbottom, a friend of Harry, Ron, Hermione, Ginny and Luna.
Katie Leung as Cho Chang, Harry's ex-girlfriend
Amber Evans and Ruby Evans as Flora Carrow and Hestia Carrow
Ashley Whitehead as an unnamed orphan
Louis Cordice as Blaise Zabini, a Slytherin boy in Harry's year.
Freddie Stroma as Cormac McLaggen, Ron Weasley's rival for the position of Gryffindor Keeper.
Isabella Laughland as Leanne, a friend of Katie Bell.
Robert Knox as Marcus Belby, a candidate for the Slug Club. Knox was murdered on 24 May 2008, before the film was released.
Tony Coburn as Young Lucius Malfoy, a former Slug Club member.
William Melling as Nigel Wespurt, A red haired boy.
Ralph Ineson as Amycus Carrow, a Death Eater.
Suzanne Toase as Alecto Carrow, a Death Eater.
Dave Legeno as the werewolf Fenrir Greyback.
Tom Moorcroft as Regulus Black, Sirius Black's brother. The only part in which he appears in the film is a moving picture in Horace Slughorn's posession.
Charlie Bennison as Sanguini, the vampire at Slughorn's party
Lord John Paul Castrianni as Yaxley, a Death Eater
Rod Hunt as Thorfinn Rowle, a Death Eater.
Afshan Azad and Shefali Chowdhury as Parvati and Padma Patil
Elarica Gallagher as Waitress.
Geraldine Somerville as Lily Evans, Harry's mother.
Alfie Enoch as Dean Thomas, a Gryffindor boy in Harry's year.
Jamie Waylett and Josh Herdman as Vincent Crabbe and Gregory Goyle, Draco's cronies.
Devon Murray as Seamus Finnigan, a Gryffindor boy in Harry's year.
Amelda Brown as Mrs. Cole, caretaker of Wool's Orphanage.
Jack Pryor and Mark Lockyer as Skinny Kid and Waiter.
Paul Ritter as Eldred Worple, author of Blood Brothers: My Life Amongst the Vampires and friend to Sanguini.
Joerg Stadler and Caroline Wildi as the Inferi, reanimated corpses at the Horcrux Cave.
Elliot Francis, Stephen Modell, and Ben Shephard as Slug Club member, Feather Wizard, and Diagon Alley Father