Jack Thorne wrote the script for Harry Potter and the Cursed Child from a story developed with J.K. Rowling and John Tiffany.
The play premiered in London’s West End in 2016. Its story is set nineteen years after the events of Harry Potter and the Deathly Hallows and follows Harry as an adult, together with his son Albus Severus Potter and Draco Malfoy’s son Scorpius.
Rowling developed the story with playwright Jack Thorne and director John Tiffany. Thorne wrote the stage script, while Tiffany directed the original production. This division of roles is why answers naming Rowling, Tiffany, or Thorne can appear in discussions about who “created” the play, but the specific answer for the scriptwriter is Jack Thorne.
The published script was marketed as the eighth official story in the Harry Potter series, but it is a play script rather than an eighth novel written by Rowling.