The show's Season 5 finale airs Tuesday.
"Within the next couple of weeks, we're going to begin shooting the last 19 episodes, which will be the final two seasons of the show," Tolan told TVGuide.com.
Created by and starring Denis Leary, the series follows a group of fictional firefighters as they deal with the aftermath of the real-life terrorist attacks on the World Trade Center Sept. 11. 2001, which killed hundreds of New York firefighters.
"I think they're stretching the airing of (the series) out until the 10th anniversary (of 9/11,)" Tolan said. "So if you put 10 episodes on next year and nine the following year, you'll land there."