Speaking to the Radio Times, Firth explained that he wouldn't be surprised if Harry didn't survive the upcoming ninth series.
"I am the anchor," he said. "My character is the obvious candidate."
Firth joked that he is worried about the final scenes of the show, saying: "The costume department has just told me that the end of episode eight involves some blood - potentially on my costume!"
Firth also revealed details of Harry's storyline in the new series.
"There is a crisis for Harry, a midlife thing," he explained. "He's questioning whether he can be a tool of the state any more if the state is operating in a way that offends his sensibilities and principles."
The new series of Spooks begins on Monday, September 20 at 9pm on BBC One.