Contract terms were not disclosed, but reports claimed it's a five-year pact worth $2-2.5 million annually.
Mangini replaces Herm Edwards, who left New York last Monday to succeed Dick Vermeil as head coach of the Kansas City Chiefs.
"He's got a strong pedigree," Jets owner Woody Johnson said of the unproven Mangini.
Eric Mangini speaks to reporters on Tuesday morning. (AP Photo/Ed Betz)
"He's been a major contributor to a very successful organization. The most important thing is he demonstrated to us a passion for football, a passion for teaching."
Mangini, who turns 35 on Thursday, will be the youngest head coach in the NFL.
"Obviously, my age is a question," he said. "But I read recently where (Super Bowl-winning head coach) Bill Walsh said you're never quite ready for your first head coaching job regardless of how old you are.
"I'm not naive to think there won't be bumps along the way. We're going to grow together."
"It's about experience and ability," added Jets general manager Terry Bradway. "It's not about age."
Mangini first hooked up with Patriots head coach Bill Belichick as an assistant with the Cleveland Browns in 1995, then wound up hired by Bill Parcells as a defensive specialist from 1997-99.
"Being compared to Bill Belichick is one of the highest compliments you can be paid," Mangini said. "I am not Bill Belichick, I am not Bill Parcells, I am Eric Mangini.
"I'm going to approach it my way. I'm going to take the experiences and the lessons that I learned from those guys and I'm going to apply that to my team."
"I know how passionate the Jets fans are," he continued. "I've been here with them and I've played against them and I'm a lot happier to be here with them."
Mangini, a Connecticut native, has worked with Belichick in 10 of his 11 pro seasons.
"I've got tremendous mentors," Mangini said. "I've worked with some of the greatest coaching minds in the NFL."
Mangini won out over several notable candidates, including former head coaches Jim Haslett and Mike Tice, both Jets offensive co-ordinator Mike Heimerdinger and defensive co-ordinator Donnie Henderson as well as Jets special-teams coach Mike Westhoff.
"I've been a coach for 11 years," Mangini said. "I've been on three Super Bowl-winning teams.
"I've been with two of the greatest football minds in NFL history. I've got an extensive foundation to build the Jets into a Super Bowl-calibre franchise."
Buffalo, Detroit, Houston, New Orleans and Oakland are still without head coaches.
with files from Sports Network
