Positioned as a prequel of sorts, "Fantastic Beasts" was inspired by a textbook used by students at Hogwarts, that will not feature Harry himself.
Rowling, posting on her Facebook page, explains the movie will instead focus on Newt Scamander, the fictional author of the fictional textbook.
"'Fantastic Beasts and Where to Find Them' is neither a prequel nor a sequel to the Harry Potter series, but an extension of the wizarding world," Rowling explains. "Newt’s story will start in New York, seventy years before Harry’s gets underway."
The movie will be the first in an expanded creative partnership between Rowling and Warner Bros.
Warner Bros. initially approached Rowling with the idea for the film, but she said she felt "very protective" of Newt Scamander's story, and "the idea of seeing [it] realized by another writer was difficult."
Instead, Rowling pitched herself as the screenwriter to Warner.
"I always said that I would only revisit the wizarding world if I had an idea that I was really excited about and this is it,” she said.
The Harry Potter books is the best-selling book series of all time, with about 450 million in sales worldwide. The eight films together are the highest-grossing movie franchise of all time, grossing more than $7.7 billion worldwide.