Alex Deuyour as himself: An 11 (nearly 12)-year-old Gryffindor and one of Harry's best friends, who is intelligent and after uses his brain to decipher things and to figure out clues. He is often the brains of the group, along with Hermione, and uses logic.

Daniel Radcliffe as Harry Potter: An 11-year-old orphan living with his unwelcoming aunt, uncle, and cousin, who learns of his own fame as a wizard known to have survived his parents' murder at the hands of the dark wizard Lord Voldemort as an infant when he is accepted to Hogwarts School of Witchcraft and Wizardry.

Rupert Grint as Ron Weasley: Harry's best friend at Hogwarts, Alex's second cousin and godbrother, and a younger member of the Weasley wizarding family.

Emma Watson as Hermione Granger: Harry's other best friend and the trio's brains.

Kate Nguyen as herself: Alex's crush and best friend who is a Gryffindor.

Matt Crocitto as himself: Alex's male best friend and confidant who is a Gryffindor.

John Cleese as Nearly Headless Nick: The ghost of Gryffindor House.

Robbie Caltrone as Rubeus Hagrid: A half-giant and Hogwarts' gamekeeper.

Warwick Davis as Filius Flitwick: The Charms Master and head of Ravenclaw House. Davis also plays the Head Goblin at Gringotts, and dubs the voice of Griphook, who is embodied by Verne Troyer.

Richard Harris as Albus Dumbledore: Hogwarts' Headmaster and one of the most famous and powerful wizards of all time.

Desiree Deuyour as herself: Alex's mother and a member of the Black family who doesn't believe in blood purity.

Ian Hart as Quirinus Quirrell: The stuttering Defense Against the Dark Arts teacher at Hogwarts. Hart also voiced Lord Voldemort, while Richard Bremmer provided his physical appearance.

John Hurt as Garrick Ollivander: A highly regarded wandmaker and the owner of Ollivanders.

Alan Rickman as Severus Snape: The Potions Master, Head of Slytherin House, and Alex's godfather and honorary uncle.

Maggie Smith as Minerva McGonagall: The Deputy Headmistress, head of Gryffindor and transfiguration teacher at Hogwarts.

Julie Walters as Molly Weasley: Ron's mother.

Additionally, Zoë Wanamaker appears as Madame Hooch, Hogwarts' flying instructor and Quidditch referee; Tom Felton portrays Draco Malfoy, Alex's first cousin, a student in Slytherin and Harry's rival. David Bradley appears as Argus Filch, Hogwarts' caretaker. Matthew Lewis, Devon Murray and Alfred Enoch portray Neville Longbottom, Seamus Finnigan and Dean Thomas respectively, three first year students in Gryffindor; James and Oliver Phelps play twins Fred and George Weasley, Ron's brothers, while Chris Rankin appears as his other brother Percy, a Gryffindor prefect, and Bonnie Wright appears as Ron's sister Ginny. Sean Biggerstaff portrays Oliver Wood, the Keeper of the Gryffindor Quidditch team; Jamie Waylett and Joshua Herdman play Crabbe and Goyle, Malfoy's minions; and Leslie Phillips voices the Sorting Hat. Elizabeth Spriggs appears as the Fat Lady, a painting at Hogwarts.