However, the actor - who plays Merlin - admitted that the rise of Arthur will be the main focus of the show.
"The magic lies in the political essences of the piece," he said. "Yes, there will be dark arts. You'll see things disappearing and changing shape, but it's really about the birth of a legend. It's [about] power [being] given to the wrong individuals, a country split by war and greed… and the assent of a pure king and noble minds."
He also revealed that he has pictures of Star Wars characters Obi-Wan Kenobi and Luke Skywalker on his dressing room wall, explaining that the pair's relationship is similar to the one shared by Merlin and the young Arthur.
"Merlin is a cross between Obi Wan Kenobi and Donald Rumsfeld," he claimed.
Fiennes also expressed regret at the cancellation of his previous science-fiction series, the ABC drama FlashForward.
"It was hugely ambitious and it's sad about it being taken off air for so long," he said. "We didn't pull it off."
Camelot is expected to premiere on Starz early next year.