Midway had handled distribution of the original game.
The expansion will be released this autumn as both a 'complete' and 'collector's edition' boxed product, with a digital download also available.
The Lord of the Rings Online: Mines of Moria Complete Edition will also include the original The Lord of the Rings Online: Shadows of Angmar game (Volume I) and all content updates released since launch. The Collector's Edition will come posters, maps, etc.
It would seem a logical move for Turbine to switch distributor, given that Time Warner led a $40 million investment round in the developer last month.
Warner Bros-owned New Line Cinema is also producing the new Hobbit movies, the first of which is due in 2011.
Jim Crowley, president and CEO of Turbine, said: "We are excited to self publish The Lord of the Rings Online: Mines of Moria and to partner with Warner Bros. to distribute the title at retail this fall. Mines of Moria introduces breakthrough content and features including our Legendary Item system that will revolutionise the way players advance and customize their unique heroes."