The $360 million trilogy, based on the books by JRR Tolkien, will be shot exclusively in New Zealand over a period of 18 months, with post-production adding the same length of time again.
At three years in the making, it will be the largest production ever to be mounted in the Southern Hemisphere.
Written by Oscar-nominated screenwriters Peter Jackson & Fran Walsh, with Philippa Boyens and Stephen Sinclair, the production will assemble an international cast, including Elijah Wood who has been cast in the lead role of Frodo Baggins.
The film company's horse wrangler, Steve Old, said he was looking for experienced riders with horses over 15 hands high to take part.
He said both horses and riders should be comfortable in large, noisy crowds.
The production will utilize over 20,000 extras' days, employ a full crew of over 300 and will feature 1200 state-of-the-art computer generated effects shots.
The first in a series of horse and rider auditions begin next weekend in Alexandra in Central Otago.