Alex Deuyour as himself: A 12 (nearly 13)-year-old British-American wizard and the brains of the group, along with Hermione.
Daniel Radcliffe as Harry Potter: A 12-year-old British wizard and Alex's godbrother and second cousin famous for surviving his parents' murder at the hands of the evil wizard Lord Voldemort as an infant, who now enters his second year at Hogwarts School of Witchcraft and Wizardry.
Rupert Grint as Ron Weasley: Harry's best friend at Hogwarts, Alex's godbrother and second cousin, and one of the younger members of the Weasley family.
Emma Watson as Hermione Granger: Harry and Alex's other friend and the group's other brains.
Kate Nguyen as herself: Alex's crush and best friend who is a half-blood.
Matt Crocitto as himself: Alex's best friend and a member of the group.
Kenneth Branagh as Gilderoy Lockhart: A celebrity author and the new Defense Against the Dark Arts teacher at Hogwarts.
John Cleese as Nearly Headless Nick: The ghost of Gryffindor House.
Robbie Coltrane as Rubeus Hagrid: The half-giant gamekeeper at Hogwarts who is framed for opening the Chamber of Secrets and is sent to Azkaban on Lucius Malfoy's orders. Martin Bayfield portrays a young Hagrid.
Warwick Davis as Filius Flitwick: The Charms teacher at Hogwarts and head of Ravenclaw House.
Richard Griffiths as Vernon Dursley: Harry's abusive Muggle uncle, who despises wizards and works as a drill company director.
Richard Harris as Albus Dumbledore: The headmaster of Hogwarts and one of the greatest wizards of the age.
Jason Isaacs as Lucius Malfoy: Draco's father and a former Hogwarts pupil of Slytherin House who now works as a school governor at Hogwarts.
Maggie Smith as Minerva McGonagall: The Transfiguration teacher at Hogwarts and head of Gryffindor House.
Gemma Jones as Madame Pomfrey: The Hogwarts nurse.
Alan Rickman as Severus Snape: Alex's godfather and honorary uncle, the Potions teacher at Hogwarts and head of Slytherin House.
Fiona Shaw as Petunia Dursley: Harry's Muggle aunt.
Julie Walters as Molly Weasley: Ron's mother.
Desiree Deuyour as herself: Alex's Auror mother who is from the House of Black.
Several actors from Philosopher's Stone reprise their roles in this film. Harry Melling portrays Dudley Dursley, Harry's cousin. James and Oliver Phelps play Fred and George Weasley, Ron's twin brothers; Chris Rankin appears as Percy Weasley, Ron's other brother and a Gryffindor prefect; and Bonnie Wright portrays their sister Ginny. Tom Felton plays Draco Malfoy, Alex's first cousin and Harry's rival in Slytherin, while Jamie Waylett, Joshua Herdman, Louis Cordice, and Genevieve Gaunt portray Vincent Crabbe, Gregory Goyle, Blaise Zabini, and Pansy Parkinson, respectively. Theodore Nott will also appear. Matthew Lewis, Devon Murray and Alfred Enoch play Neville Longbottom, Seamus Finnigan and Dean Thomas, respectively, three Gryffindor students in Harry's year. David Bradley portrays Argus Filch, Hogwarts' caretaker, and Sean Biggerstaff as Oliver Wood, the Keeper of the Gryffindor Quidditch team. Leslie Phillips voices the Sorting Hat. Eleanor Columbus, Chris Columbus's daughter, appears as Susan Bones, Edward Randell appears as Justin Finch-Fletchley, Charlotte Skeoch as Hannah Abbott, and Louis Doyle as Ernie MacMillan; Hufflepuff students. Emily Dale appears as Katie Bell, Rochelle Douglas as Alicia Spinnet, and Danielle Tabor as Angelina Johnson; Gryffindor girls. Jamie Yeats appears as Marcus Flint, Scott Fearn as Adrian Puyce; and David Holmes, David Massam, and Tony Christian appear as Slytherin quidditch players. Gemma Padley appears as Penelope Clearwater, a Ravenclaw student and Percy's girlfriend. Luke Youngblood plays Lee Jordan, the Quidditch commentator.
Christian Coulson appears as Tom Marvolo Riddle, a manifestation of young Lord Voldemort. Mark Williams portrays Arthur Weasley, Ron's father. Shirley Henderson plays Moaning Myrtle, a Hogwarts ghost. Miriam Margolyes appears as Pomona Sprout, Hogwarts' Herbology professor and head of Hufflepuff. Hugh Mitchell portrays Colin Creevey, a first year student that is a fan of Harry's. Robert Hardy appears as Cornelius Fudge, the Minister for Magic. Toby Jones voices Dobby, a House-elf, while Julian Glover voices Aragog, an acromantula. Alfred Burke appears as Headmaster Armando Dippet in a memory of Tom Riddle. Daisy Bates, David Tysall,and Peter Taylor appear as moving pictures. Helen Stuart plays Millicent Bulstrode, an Slytherin girl.