The actor will appear as the Comte de Rochefort in the next series of the show, based on the stories by Alexandre Dumas, which is being filmed in Prague now.
He said: "I'm delighted to be part of the BBC's stylish and exciting take on the Dumas classic. Once I've overcome my fear of horses, I'm sure it'll be a walk in the park."
The first series pulled in around 6 million viewers for each episode and has been sold to 78 countries around the world - including France.
BBC executive producer Jessica Pope said Warren is "a clever and mercurial actor who will bring danger and charm to the role of Rochefort in equal measure".
The show will have to do without Peter Capaldi - who played Cardinal Richelieu - who quit the show to concentrate on his new role as Doctor Who.