The movie was to have been released this year under the title, "The Hobbit: There and Back Again," but has been re-named "The Hobbit: The Battle of the Five Armies," the New Zealand filmmaker said on his Facebook page.
It is due for release in America on December 17, bringing to a climax the story started in 2012's "The Hobbit: An Unexpected Journey" and last year's "The Hobbit: The Desolation of Smaug."
"Our journey to make The Hobbit Trilogy has been in some ways like Bilbo's own, with hidden paths revealing their secrets to us as we've gone along," the Oscar-winning director said.
"'There and Back Again' felt like the right name for the second of a two film telling of the quest to reclaim Erebor, when Bilbo's arrival there, and departure, were both contained within the second film.
"But with three movies, it suddenly felt misplaced -- after all, Bilbo has already arrived 'there' in the 'Desolation of Smaug.'"
Jackson said he broached the issue with studio giant Metro-Goldwyn-Mayer last year.
"We decided to keep an open mind until a cut of the film was ready to look at," he said.
"We reached that point last week, and after viewing the movie, we all agreed there is now one title that feels completely appropriate. And so: 'The Hobbit: The Battle of the Five Armies' it is."
"There and Back Again" was the subtitle of the classic epic fantasy book by J.R.R. Tolkien, published in 1937. It was followed in the mid 1950s by the "Lord of the Rings" trilogy, which Jackson also made into a blockbuster franchise, before the "Hobbit" films.
Jackson came under fire from some quarters in 2012, when the first film "The Hobbit: An Unexpected Journey" was released, for breaking the relatively short book into a trilogy.
The director won three Oscars -- best picture, best director and best adapted screenplay -- for the 2003 film "The Lord of the Rings: The Return of the King," the final part of that trilogy.