Casting directors for HBO's Harry Potter series held over 40 thousand auditions for the roles of Harry, Ron, and Hermione. The creators revealed this in a special episode, "Finding Harry: Behind the Scenes of Magic," dedicated to the 25th anniversary of "Harry Potter and the Philosopher's Stone."

According to casting directors Emily Brockmann and Lucy Bevan, children from all over the UK initially submitted online video auditions, followed by in-person auditions in major cities across the UK and Ireland. Alastair Stout, who plays Ron Weasley, auditioned in Manchester; according to the casting directors, they found him "charming and funny from the very first minute." Arabella Stanton, cast as Hermione Granger, read a poem at her London audition and then performed a comedic scene, demonstrating her ability to be both serious and wry. Dominic McLaughlin, cast as Harry Potter, auditioned in Glasgow: he read his own poem about a weekend and immediately attracted attention with his "quiet confidence."

Lucy Bevan noted that when casting the lead actor, the team focused on specific character traits: "mistrust of the adult world," "vulnerability, melancholy, and a sense of loneliness." Emily Brockmann added that the task was particularly challenging because the character of Harry Potter is so relatable to audiences worldwide.

The first season of the series will premiere on the HBO Max streaming service and HBO on December 25, 2026. The first season will consist of eight episodes. Filming for the first season, based on the novel Harry Potter and the Philosopher's Stone, began in July 2025 at Leavesden Studios, England—the same location where the original Harry Potter films were filmed. The series is based on the novel series of the same name by British author J.K. Rowling. The story follows the boy wizard Harry Potter, who at eleven years old discovers his magical heritage and enrolls at Hogwarts School of Witchcraft and Wizardry, where he and his friends Ron Weasley and Hermione Granger confront the dark wizard Lord Voldemort. Unlike the original film saga, the new project is conceived as a seven-season adaptation of all the books in the series—one season for each.