The Lord of the Rings director last month confirmed rumours that there were plans to turn what was initially a two-part story into a trilogy.
According to The Wrap, the third Hobbit film - now titled There and Back Again - will debut worldwide on July 18, 2014.
Head of distribution for Warner Bros Dan Fellman said that the summer release was because "opening in July affords us not only the perfect summer tentpole, but fans will have less time to wait for the finale of this epic adventure".
The first film, The Hobbit: An Unexpected Journey, is to be released on December 14, while the second film - now titled The Desolation of Smaug - opens on December 13, 2013.
Smaug the dragon is portrayed by Sherlock star Benedict Cumberbatch, who recently confirmed that his role is much more prominent in the second instalment, saying: "I think my eye might open at the end of the first film, and then you'll get the rest of me in the second."
Watch the trailer for The Hobbit: An Unexpected Journey below: