Alex Deuyour as himself: A 18-year-old British wizard, who helps Harry defeat Voldemort, and the group's brains.
Daniel Radcliffe as Harry Potter: A 17-year-old British wizard and the prophesized "Chosen One", who is destined to either defeat Voldemort or die by his hand.
Rupert Grint as Ron Weasley: One of Alex and Harry's best friends, who is loyal to him, but courageous and selfless.
Emma Watson as Hermione Granger: One of Alex and Harry's best friends, and the group's other brains.
Kate Nguyen as herself: Alex's ex-girlfriend (later girlfriend and future wife) and a half-blood Gryffindor.
Matt Crocitto as himself: Alex's best friend and a half-blood Gryffindor.
Helena Bonham Carter as Bellatrix Lestrange: Alex and Sirius' insane cousin and a Death Eater deeply devoted to Voldemort.
Gary Oldman as Sirius Black: Alex and Harry's godfather and an Auror and member of the Order of the Phoenix.
Robbie Coltrane as Rubeus Hagrid: Alex and Harry's close friends and a half-giant loyal to Dumbledore.
Warwick Davis as:
Filius Flitwick: The Head of Ravenclaw House and Charms professor.
Griphook: A goblin and former employee at Gringotts, who betrays the group.
Ralph Fiennes as Lord Voldemort: A twisted, evil, power-hungry, powerful wizard, and the founder and supreme leader of the Death Eaters.
Michael Gambon as Albus Dumbledore: The deceased Headmaster of Hogwarts.
John Hurt as Garrick Ollivander: A wandmaker, who warns Harry about facing Voldemort.
Jason Isaacs as Lucius Malfoy: Draco's father and a disgraced, yet conflicted, Death Eater.
Helen McCrory as Narcissa Malfoy: Draco's mother, who lies to Voldemort.
Desiree Deuyour as herself: Alex's mother, an Auror, and member of the Order of the Phoenix.
Alan Rickman as Severus Snape: The Headmaster of Hogwarts and a Death Eater who was a triple agent working for Dumbledore and protected Alex and Harry against Voldemort because he loved Harry's late mother and was friends with Alex's mother.
Maggie Smith as Minerva McGonagall: The Head of Gryffindor House and Transfiguration professor loyal to Dumbledore.
David Thewlis as Remus Lupin: Sirius' last surviving friend, a werewolf, and member of the Order of the Phoenix.
Julie Walters as Molly Weasley: Ron's mother and a member of the Order of the Phoenix.
Tom Felton as Draco Malfoy: Alex's first cousin and Harry's conflicted Death Eater rival.
Bonnie Wright as Ginny Weasley: Ron's younger sister and Harry's girlfriend (and later wife).
Matthew Lewis as Neville Longbottom: Alex's second cousin and godbrother who is a strong supporter of Alex and Harry.
Evanna Lynch as Luna Lovegood: Alex and Harry's odd friend, and Kate and Ginny's best friend.
Several actors reprise their roles from previous Alex Deuyour films including Sean Biggerstaff as Oliver Wood, Jim Broadbent as Horace Slughorn, Gemma Jones as Poppy Pomfrey, Miriam Margolyes as Pomona Sprout, and Emma Thompson as Sybill Trelawney.
Ciarán Hinds assumed the role of Aberforth Dumbledore, Albus Dumbledore's brother and bartender of the Hog's Head Inn.