Ruff, who had been an assistant with the New York Rangers since 2017, replaces interim coach Alain Nasreddine, who guided the team to a 19-16-8 record after John Hynes was fired on Dec. 3. Fitzgerald had served as interim general manager since Ray Shero was fired on Jan. 12.
"It was evident that Tom was the right person for this job," co-owner David Blitzer said, citing Fitzgerald's work at the February trade deadline and beyond. "We're very excited to remove that interim tag."
The Devils posted a 28-29-12 overall record, missing the playoffs for the seventh time in eight years. Their season was halted by the coronavirus pandemic in early March, and they were not among the 24 teams chosen to compete for the Stanley Cup when NHL play resumes.
During the pause, the Devils interviewed Nasreddine and former head coaches Gerard Gallant, Peter Laviolette and John Stevens. The process was extensive, with Zoom interviews that lasted upward of five hours. They were "deep dives" on the coaches' systems and how they meshed with the way Fitzgerald felt the team should play.
"As the process moved forward, Lindy just continued to step to the forefront," Fitzgerald said. "I was looking for NHL head-coaching experience; for someone that could walk into a room and grab the attention of our young team [because] the group needs a teacher. The more we kept digging, the more Lindy kept rising."
Once Fitzgerald felt Ruff was the front-runner, he put the coach in front of franchise legend Martin Brodeur, who was serving in an advisory role in hockey operations. After that, the choice went to owner Josh Harris and Blitzer for the final sign-off.
The head-coaching job is the third in the NHL for the 60-year-old Ruff. He coached the Buffalo Sabres and Dallas Stars, leading the Sabres to the Stanley Cup Final in 1999. He was hired by the Rangers before the 2017-18 season. He has a 736-554-78-125 record, with 10 playoff appearances.
A former defenseman, Ruff played in 691 NHL regular-season games and had 105 goals and 195 assists. He also appeared in 52 playoff games.
Ruff has been coaching in the NHL since 1993, when he was an assistant with a Florida Panthers team that Fitzgerald played on. He said that his reputation as a coach has changed depending on the way he needed his players to play.
"I've had teams where I was criticized for coaching too defensive. Then I've had teams where I've been criticized for coaching too offensive," he said.
Ruff was known in the past for his intensity as a head coach, but he said that as times have changed, so have tactics.
"I've told players in the past [not to] get caught up in my emotion but get caught up by the message," he said. "Those days of just walking in there and screaming and yelling ... the players want to know the 'why' part."
Fitzgerald said current Devils coaches will have a chance to meet with Ruff and discuss their futures. That includes assistant coach Mike Grier, who played for Ruff with the Sabres, as well as Nasreddine. Fitzgerald said Nasreddine "has proven to be one of the best penalty-kill coaches in the league, which is a thing we need."
Gord Murphy, an associate coach with the AHL Hartford Wolf Pack, will replace Ruff behind the Rangers' bench during the 24-team tournament this summer.
Information from ESPN's Emily Kaplan, Greg Wyshynski and The Associated Press was used in this report.