The decision was taken so that the film could remain true to the final JK Rowling novel, without having to leave anything out.
The two films will be directed by David Yates, who previously looked after the fifth film, Harry Potter and the Order of the Phoenix, and is currently working on film number six, Harry Potter and the Half-Blood Prince.
This will be the first time that any director will helm more than two releases in the Harry Potter film franchise.
Jeff Robinov, president of Warner Bros Pictures Group, commented: "In concluding the film franchise, we recognised that Harry Potter and the Deathly Hallows is packed with vital plot points that complete the story arcs of all of its beloved characters.
"That said, we feel that the best way to do the book, and its many fans, justice is to expand the screen adaptation and release the film in two parts."
Part one of Harry Potter and the Deathly Hallows will be released in autumn 2010, with part two following in summer 2011.