"You can't hold back progress," Rowling said. "E-books are here and they are here to stay."
The magical stories that conquered the world in print form will be available as audiobooks and e-books in multiple languages exclusively through a new interactive website, "Pottermore."
Rowling, one of the world's most powerful authors, is bypassing established online retailers like Amazon, although the creators of Pottermore say the books will be compatible with popular e-readers including Amazon's Kindle, Sony's Reader and Apple's iPad.
"It's very important to Jo to make the books available to everybody, not to make them available only to people who own a particular set of devices, or tethered to a particular set of platforms," said Tom Turcan, chief operating officer of the new venture, Pottermore Ltd.
He said prices for the e-books would be announced closer to October.
The site is a partnership with Sony Corp. and its online shop is described as "a potential outlet for Sony products." Rowling spokesman Mark Hutchinson said Sony was selected as "the most appropriate partner."
Rowling also has written 18,000 words of new Potter material for the site, which promises to immerse users in her world of wizards, combining elements of computer games, social networking and an online store. She says the site includes "information I have been hoarding for years" about the books' characters and settings.
"Pottermore" has been the subject of intense speculation among Potter fans since it appeared on the Internet with the words "coming soon."
The project unveiled in London lets Potter fans delve into the world of Hogwarts School of Witchcraft and Wizardry. Sections let users shop for wands in Diagon Alley, travel to Hogwarts from the imaginary Platform 9 3/4 at London's King's Cross train station and be sorted into Hogwarts school houses by the perceptive Sorting Hat.
Along the way are wand fights, games and new information about characters beloved around the world, including Harry's reviled relatives, the Dursleys.
The site goes live July 31, when 1 million registered users will be chosen through an online competition to help flesh out the Pottermore world. It will be open to all users from October, in languages including English, French, German and Spanish.
"(It's) a way I can be creative in a medium that didn't exist when I started the books back in 1990," Rowling told reporters. She said it was a way to incorporate the thousands of "stories, drawings, ideas, suggestions" she still receives from fans four years after the last Potter book was published.
Harry Potter fans who have been sharing their enthusiasm online for years should be delighted by the new digital world. But Rowling said she wanted to keep the emphasis of the site firmly on the written word.
"We've had a lot of requests for online games," she said. "I wanted to pull it back to reading."
The seven Harry Potter novels have sold more than 450 million copies and made Rowling one of the world's richest women.
The last book, "Harry Potter and the Deathly Hallows," was published in 2007, and Rowling said she still has no plans to write an eighth. But she said Pottermore was a way to reconnect with a character and a universe she loved.
"It is exactly like an ex-boyfriend," Rowling said. "Finishing writing Harry -- I have only ever cried in that way and that much when my mother died. I have never cried for a man the way I cried for Harry Potter."
There may yet be another Potter book -- a long-anticipated encyclopedia. Rowling said she was still considering compiling one, with the proceeds going to charity.
"Will there ever be an encyclopedia?" Rowling said. "Possibly."
The final Harry Potter film, "Harry Potter and the Deathly Hallows, Part 2," has its world premiere in London on July 7. Hutchinson said timing of the website announcement had nothing to do with the Warner Bros. movies.