JK Rowling to pen first adult novel
The book will be published worldwide, although no date or title has yet been released.
"The freedom to explore new territory is a gift that Harry's success has brought me," Rowling said.
The writer published seven Potter books, which have sold more than 450 million copies around the world.
The books, about a boy wizard, became a worldwide phenomenon and were turned into eight blockbuster films starring Daniel Radcliffe.
When the final instalment of the book series went on sale in 2007, thousands of copies sold in minutes.
All the Potter books were published by Bloomsbury, but Rowling has chosen a new publisher for her debut into adult fiction.
"Although I've enjoyed writing it every bit as much, my next book will be very different to the Harry Potter series, which has been published so brilliantly by Bloomsbury and my other publishers around the world," she said, in a statement.
"The freedom to explore new territory is a gift that Harry's success has brought me, and with that new territory it seemed a logical progression to have a new publisher."
"I am delighted to have a second publishing home in Little, Brown, and a publishing team that will be a great partner in this new phase of my writing life."
Little, Brown's David Shelley said the company were "thrilled, honoured and proud" to be publishing Rowling's latest novel.
"For me, quite simply, it is a personal and professional dream come true to be working with JK Rowling."
So as of yet no word on what the book(s) will be about but she is sure it will have an adult theme.