Mattison coached with new Wolverines coach Brady Hoke under Jack Harbaugh at Western Michigan and Lloyd Carr at Michigan.
Pagano will be officially introduced as the defensive coordinator at a news conference Wednesday.
"He's completely, in my view, a great coach and deserves it," Ravens cornerback Josh Wilsontold the Carroll County Times. "He knows what he's doing. Chuck is going to be a great defensive coordinator. It's not going to be any kind of, 'Can he get the job done?' Everybody knows he can handle it. It's going to be like nothing ever changed."
Cornerback Fabian Washington, who has played under Pagano for five years (two in Oakland), called the move "way past overdue."
"Chuck is the right guy for the job," Washington told The Baltimore Sun. "If anybody deserves that job, it's Chuck. That guy is one of the best football coaches I've ever been around."
The Associated Press contributed to this report.