Carroll ended his nine-year tenure with the Trojans on Monday, signing what NFL Network's Michael Lombardi reports is a five-year, $35 million contract to return to the NFL as coach of the Seahawks.
"If you know anything about me, you know I can't pass up this challenge," Carroll said.
Carroll's hiring capped a busy weekend for Seahawks chief executive Tod Leiweke. The team fired coach Jim Mora on Friday after only one season, and Leiweke spent Sunday in Southern California completing a deal with Carroll.
"We are excited to add Pete as our coach," Leiweke said in a statement released by the team. "He brings a great passion for winning and a positive attitude that is contagious."
The Seahawks are expected to formally introduce Carroll at their headquarters in Renton, Wash., on Tuesday.
Earlier Monday, Carroll told The Los Angeles Times that he was surprised to receive another opportunity in the NFL.
"I had given up on it," Carroll said, "but it came out of nowhere."
Carroll comes to a Seattle team that's coming off a 5-11 season.
"We now turn our full attention to the hiring process for a general manager," Leiweke said in the statement. "Our intended structure is for Pete and the new GM to work in a collaborative capacity on football matters."
The Seahawks are searching for a general manager after forcing president and GM Tim Ruskell to resign Dec. 3.
How much control Carroll would have over football operations was a key issue throughout his negotiations with the Seahawks. However, league sources told NFL Network's Jason La Canfora over the weekend that the Seahawks informed GM candidates that their title and authority wouldn't be impacted by a coaching hire and the position would include roster control.
Lombardi reported Sunday that Floyd Reese, the Patriots' senior football advisor and a former Tennessee Titans GM, plans to meet with the Seahawks this week. Other candidates include Pittsburgh Steelers front-office executive Omar Khan, Green Bay Packers director of football operations John Schneider and New York Giants director of college scouting Marc Ross.
Former Indianapolis Colts coach Tony Dungy turned down an offer to become the Seahawks' team president, said Fritz Pollard Alliance chairman John Wooten, who monitors the NFL's minority hiring practices.
"They called Tony about three weeks ago to see if he would seriously consider becoming their president," Wooten told ESPN on Monday night. "He told them he wanted to pray and sleep on it, but the next day, he called them back and said he wanted to stick with everything he was doing now. He would have been the guy, I believe, if he had wanted to do it."
USC freshman quarterback Matt Barkley said quarterbacks coach Jeremy Bates is leaving with Carroll after only one season, presumably to become the Seahawks' offensive coordinator. Bates previously had been linked to the Chicago Bears' offensive coordinator job because he coached quarterback Jay Cutler when he was with the Denver Broncos.
At least two other USC assistants -- assistant head coach for defense Ken Norton and offensive line coach Pat Ruel -- are expected to be on Carroll's Seahawks staff, The Associated Press reported.
Carroll won 97 games, seven Pac-10 titles and two BCS national championships at USC, but the school is under a cloud of NCAA investigation and other scandals. Although the charismatic coach glowingly spoke of his highly successful years in Los Angeles, he jumped at the best -- and timeliest -- of the many offers he has received over the years to return to the NFL.
However, Carroll insisted that his decision had nothing to do with the NCAA's lengthy look into his program, denouncing rumors of a rift between him and USC athletic director Mike Garrett. Carroll said he believed he would be with the Trojans "forever."
But Seahawks owner Paul Allen pried the 58-year-old coach out of a comfortable oceanside life as one of the most popular sports figures in the nation's second-largest media market, with numerous charity endeavors and a team that helped fill the area's NFL void.
Garrett refused to divulge his list of candidates to replace Carroll, but one coach who has been linked to the job is Jack Del Rio, who played at USC. The Jacksonville Jaguars' coach is scheduled to meet with team owner Wayne Weaver on Tuesday, and Sports Illustrated's Peter King reported Monday that Del Rio is calling assistant coaches who might want to be on his staff should be fired and receive the USC job.
The Florida Times-Union cited a high-ranking source Monday night in reporting that Del Rio's job in Jacksonville is safe. He has three years and $15 million remaining on his contract.
The Associated Press contributed to this report.