He told Entertainment Weekly that the new run will expand on events in the first season and hinted at a number of character deaths.
"In true Spartacus fashion, nothing will be easy for our heros and villains," he claimed. "The scope and scale we are attempting is much larger than anything we have done before. And I'm guessing a few beloved characters may die."
DeKnight also confirmed that Gannicus (Dustin Clare) will appear in the new season, having survived the events of prequel series Gods of the Arena.
"Gannicus is one of Spartacus's generals in the actual war," he explained. "Our original plan was always to introduce Gannicus into [the main] storyline. We will set him up to at some point come back [but] he won't pop up immediately."
He added that the series could run for a total of "anywhere from three to six seasons".
"One [issue] is budget," he said. "The show gets more expensive each season. The other is ratings.
"Budget is not a small part of it. As the gladiator war continues and Spartacus's army grows, it becomes more difficult to produce on a TV budget."
Spartacus: Vengeance is now expected to air on Starz in January 2012.