The novel is expected to run to close to 500 pages, and will appear in hardback as well as in e-book format and audiobook.
The Casual Vacancy focuses on the town of Pagford, with its cobbled square and ancient abbey, which is left in shock when parish councillor Barry Fairweather dies unexpectedly in his early forties.
The publishers said: "What lies behind the pretty facade is a town at war.
"Rich at war with poor, teenagers at war with their parents, wives at war with their husbands, teachers at war with their pupils."
The story follows the battle for the empty seat on the parish council "in an election fraught with passion, duplicity and unexpected revelations".
In February, Rowling said: "Although I've enjoyed writing it every bit as much, my next book will be very different to the Harry Potter series."
A spokesman for Waterstones said it was "wonderful to finally know the title and release date" of the book.
The first Harry Potter book was released in 1997, with the seventh and last published a decade later. It became the bestselling book series in history, shifting more than 450 million copies around the world, and turned into eight blockbuster films which brought in billions of dollars at the box office.
Last month, Pottermore, the digital venture that publishes the Potter e-books, went live and sold more than £1 million ($1.9 million) worth of electronic books about the teenage wizard in just three days, smashing expectations.
The operation's director, Charlie Redmayne, said: "Everything that Harry Potter does surpasses expectations."
Rowling turned her back on Potter publisher Bloomsbury, saying that with the new direction of her work "it seemed a logical progression to have a new publisher".
- Independent