Mastromatteo's commitment comes a couple of days after the 6-foot-1, 215-pound linebacker from Absecon (N.J.) Holy Spirit visited UNC.
"I was down there Wednesday and Thursday and I felt like I fit in well there and I loved it," Mastromatteo said. "The academics were top notch. The coaching staff, I feel like is definitely one of the best coaching staffs around [and] I could learn a lot from them."
Heading into the visit, Mastromatteo was favoring Rutgers.
"When I was up [at UNC] I loved the dorms and everything about it," Mastromatteo said. "The defensive scheme, I feel like I'll fit in great. [UNC] was just the perfect match."
In addition to UNC and Rutgers, Mastromatteo collected scholarship offers from Boston College, Cincinnati, Illinois, Maryland, Michigan State, NC State, and Temple.
"I wanted to make a commitment early and I knew if I felt good about a place I would do it," Mastromatteo said. "So I didn't want to waste any time."
Mastromatteo says his pledge to UNC is solid.
"I'm not going to do any more visits or anything," Mastromatteo said.
On Wednesday, Mastromatteo toured UNC's campus and spent time with the UNC coaching staff, including linebackers coach Art Kaufman.
"[Kaufman] just went over the scheme with the defense, and how their linebackers play and the techniques they teach them," Mastromatteo said. "He said I'd fit in great there."
Most of Thursday was spent seeing the academic side of UNC.
"I'm going to go into [UNC] undecided," Mastromatteo said. "[UNC] is a great school for me going in undecided as a liberal arts major. I can go in there and have two years to decide what I'm going to major in, so that's great."
Before heading home on Thursday, Mastromatteo met with Butch Davis.
"He said he loves the way I play and the way I fit into this scheme," Mastromatteo said. "We just talked about the recruiting process, a little stuff about football, and about life."