Poulter, who joined the big-budget series in September, has departed the project due to scheduling conflicts, a source told Variety.
Details about Poulter’s character had not been disclosed, but he was set to play a lead role in the show, which was based on JRR Tolkien’s novels.
As it stands, the show’s cast includes Game of Thrones star Joseph Mawle, who is playing the central villain, Markella Kavenagh and Ema Horvath.
The Amazon series will go into production in 2020 in New Zealand, the filming location of Peter Jackson’s Lord of the Rings film trilogy.
It is estimated to cost $1bn and is being developed by the Star Trek 4 writing team of JD Payne and Patrick McKay. Game of Thrones screenwriter Bryan Cogman has signed on as a consultant on the project with JA Bayona (Jurassic World: Fallen Kingdom) set to direct multiple episodes.
The show will be set during the Second Age of Middle-Earth and will serve as a prequel to the events of both the film trilogy and the source novels.