PHOENIX – When last season ended, it was plausible to suspect James Harrison hadn't played his last snap for the Steelers, and that he might be returning again this season sooner or later.

As it turned out it was sooner rather than later.

Harrison, who will turn 37 on May 4, has signed a two-year contract and will return in 2015 for his 12th season with the Steelers and his 13th in the NFL.

"We actually thought about that," General Manager Kevin Colbert said of delaying Harrison's eventual return, a move that would have saved Harrison offseason reps and provided maximum opportunity to develop young players at the outside linebacker position. "But the values that he provides right now for those young guys we think trumps waiting.

"He's valuable in the building right now. He's been in the building voluntarily since really the end of the season. It's been amazing to watch. And those young guys see it and they're like, 'OK, I think I'm supposed to do that, too.' They're all kind of following his lead.

"I really think he's taken on a mentorship role and seems to really be enjoying it, and I think that's important. Plus, we think he can still help us on the field, for sure."

Harrison is the second member of last season's corps of linebackers to return to the Steelers. Arthur Moats agreed to terms on March 9. Jason Worilds has retired.

Harrison had retired after spending 2013 with the Cincinnati Bengals but re-signed with the Steelers last Sept. 23. He wound up appearing in 11 games, starting three, and finishing third among Steelers with 5.5 sacks, two behind co-leaders Cam Heyward and Worilds (7.5 each).

Harrison also started the Steelers' playoff loss to Baltimore.

"That's Coach (Mike) Tomlin's call, but I would imagine (Moats would be penciled in as the starter at left outside linebacker)," Colbert said. "It'll be an open competition (at right outside linebacker between Jarvis Jones and Harrison). It'll be a good competition.

"And with Coach (Keith) Butler now coordinating the defense, there may be some different combinations and alignments they use. I think they'll wait and see the group of players that they're playing with come the spring, see what they have and how they can work them all together. "

Harrison had said upon rejoining the Steelers last September that the 2014 season would be his last. But he emerged from the campaign in January thinking he might have football yet left in him.

"My body felt better, to be honest with you," Harrison said. "The first few weeks, it was a feeling of my body couldn't take this, it couldn't handle this. Over the course of the first three to four weeks or so my body adjusted, started to feel a lot better. I felt better at the end of the year than I did in the previous probably two, three years. That was something that crept into my head, 'You know I'm actually feeling good. It's nowhere near what I thought I would feel.'"

Harrison's role and productivity expanded after his frame contracted via the loss of "20, 30 pounds" during his first month back with the Steelers last season. Harrison had anticipated as much upon committing to a return.

"They told me I would be filling in a few snaps here and there, 20 or so snaps (a game)," Harrison said. "I felt like I could start. I'm not coming into any situation thinking I'm just going to stick to that role. No guy comes into any situation thinking he's going to just stick to that role. His anticipation or his desire is to start, and that's what it was."