Roof will replace former coordinator Al Groh, who was fired midseason, and interim coordinator Charles Kelly, who is expected to be hired at Florida State, according to a source. Penn State coach Bill O'Brien promoted secondary coach John Butler to defensive coordinator, replacing Roof.
"I've known Ted for a long time and I'm excited that he has decided to come back to Georgia Tech," coach Paul Johnson said in a prepared statement. "He's one of the most respected football coaches in the nation."
Roof's hiring cannot become official until Georgia Tech has completed a background check, which likely will not occur until next week, according to the school's release.
Roof's hire was somewhat of a surprise, considering how close he and O'Brien are, but there had recently been some uncertainty surrounding O'Brien's future at Penn State, and Roof has significant ties to his alma mater.
"John did an outstanding job with the secondary this past season and brings tremendous experience, energy and a passion for tenacious defense to the field and in the meeting room," O'Brien said in a statement. "John quickly developed a great relationship with all our players on defense and special teams and his ability to teach and relate to the players on and off the field will greatly assist in making this an easy transition.
"I am very appreciative of Ted's contributions to Penn State. Ted and I have known each other a long time and coached together at Georgia Tech, his alma mater. Ted is a great coach and person. He earned the respect of our players and they enjoyed playing for him. We wish Ted and his family well."
Roof, a native of Lawrenceville, Ga., was a four-year letterwinner as a linebacker under coach Bill Curry from 1982-85. As a senior, he was co-captain and a first team All-ACC selection on a team that finished 9-2-1 and defeated Michigan State in the All-American Bowl. Roof is in the Georgia Tech Athletics Hall of Fame.
He returned to Georgia Tech in 1998 to serve as linebackers coach under coach George O'Leary. He was promoted to defensive coordinator in 1999 and held that position for three years. The Yellow Jackets shared an ACC title in 1998 and played in a bowl game all four years during Roof's tenure.
This past season, the Nittany Lions' defense ranked second in the Big Ten in scoring defense (19.1 ppg), first in sacks (34), first in red-zone defense and third in turnover margin. Two of the Big Ten's top six tacklers were Nittany Lions -- Gerald Hodges and Michael Mauti.
Outside linebacker Brandon Bell, an incoming Penn State recruit, was surprised to see Roof leave.
"You know, it's definitely a shocker," Bell told NittanyNation's Josh Moyer. "I'm still trying to bring it all in, but I do like coach Butler. So it's a little better than bringing in a new guy, but I had a good relationship with Roof."
In 2010 at Auburn, Roof's defense ranked ninth nationally in rushing defense and 16th in tackles for loss. In the Discover BCS National Championship, the Tigers (14-0) held Oregon to 19 points -- 28 points below the Ducks' season average.
Roof's familiarity with the ACC extends beyond Georgia Tech. From 2004 to 2007, Roof was coach at Duke after working as the Blue Devils' defensive coordinator in 2002 and 2003. He was promoted to interim coach midway through the 2003 season after coach Carl Franks was fired.
Roof will inherit a defense that returns eight starters and is coming off a Hyundai Sun Bowl win over USC.
Information from NittanyNation's Josh Moyer was used in this report.