"Perry has done a great job with our defense and has demonstrated excellent leadership skills as defensive coordinator," Bills owner Ralph Wilson said in a statement. "Our players and staff have a lot of confidence in him and that is important as we look forward to these next seven games."
At a Tuesday evening news conference to introduce the new interim coach, Fewell shared a simple but blunt philosophy in taking over after Jauron was abruptly fired.
"Play like hell and win," Fewell said.
That's the plan and also the challenge for Fewell, following the defensive coordinator's promotion. He has seven games left in the season to prove that he's capable of turning around a struggling team and a franchise that's now on its fifth coach in nine years and in jeopardy of missing the playoffs for a 10th straight season. The Bills -- who are celebrating their 50th season -- are tied with the Lions for the longest active streak of non-playoff seasons.
Fewell then showed he's smart enough to not make any guarantees, when asked to assess how much he can do to fix an offense that's sputtered for most of the season despite the presence of Terrell Owens.
"We are who we are," Fewell said, adding he'll wait until Wednesday to announce whether Trent Edwards or Ryan Fitzpatrick will start at quarterback this weekend. "We have that identity. We're going to try to give a little spark, but we are who we are."
Wilson described his decision to change coaches as a difficult one, but one "for the best interest of our team."
"I really don't have anything to say," was all Jauron would say when reached on his cell phone by The Associated Press.
In electing to promote Fewell, Wilson credited the assistant for having done "a great job with our defense and demonstrated excellent leadership skills," while noting the players and staff have confidence in him.
Fewell is in his 12th NFL season, and fourth with Buffalo as the team's defensive coordinator, after being hired by Jauron, whose background is primarily on the defensive side. Fewell also becomes the team's first black head coach.
He was offered the job by Wilson, shortly after he and the coaching staff were informed by Jauron that he had been fired.
Fewell declined to discuss whether he's been given an opportunity to keep the job beyond this season, but called his promotion "the opportunity of a lifetime."
The Bills' defense under Fewell has shown a resilient quality, though the numbers don't always show it. The unit's best season under Fewell was last year, when it finished 14th in the NFL in yards allowed despite missing numerous players to injuries.
Things haven't been better on the injury front this season. The defense ranks 26th in the NFL yards allowed, but Fewell has made do with a unit that's played with as many as six regulars out of the lineup, including two starters on injured reserve.
The defense, which is allowing an average of 173 yards rushing, has been credited for keeping the Bills competitive. Buffalo has either led, been tied or been within a score of the lead entering the fourth quarter in all of its games except for a 38-10 loss at Miami on Oct. 4.
The trouble has been the inept offense that's averaging just over 15 points, is unsettled at quarterback and features an inexperienced line.
So much for the spark Owens was supposed to provide after he signed a one-year $6.5 million contract in March, days after the receiver was released by Dallas.
Receiver Lee Evans expressed his support for Fewell, and doesn't mind his defensive background, saying "I don't think that plays into it."
"The way our defense is playing with all the injuries, it's a testament to him. They've done a great job of keeping us in games," Evans told The AP. "I think this is a great opportunity for him. ... I think he should try to stick with the things that made him the coach he is, rally the team and keep us on the same page."
Jauron has been on the hot seat ever since last season, after he led the Bills to their third consecutive 7-9 finish.
Defensive end Chris Kelsay was shocked to learn of the move happening this late in the season, but not entirely surprised. Kelsay was well aware before the start of the season that changes were in store if the Bills faltered.
"I think everybody understood this was a big year and there was lots at stake," Kelsay told the AP, adding he maintains his respect for Jauron. "I feel a little responsible for it, and most players do. I feel like I let him down because we, as players, are the ones to blame."
The Associated Press contributed to this report.