The 50-year-old author took to Twitter and shared the news with her 5.57 million followers.
"*Clears throat loudly and bangs teaspoon on mug of tea* I have #CursedChild news!
"Due to the epic nature of the story we've been working on, Harry Potter & the #CursedChild will be in two parts! @HPPlayLDN," she tweeted.
Director John Tiffany said he was exited to tell a story which "one one yet knows," said The Hollywood Reporter.
"I've never worked on anything quite like this before. Usually in theatre you're adapting existing material or creating an entirely new play.
Part one of the play is scheduled to open in London's West End in the summer of 2016.
Rowling has said the story was always intended as a play where Harry is not the cursed child and the story is not a prequel. Plot details have been kept under wraps.