Carroll ended his nine-year tenure with the Trojans on Monday, leaving behind a program facing multiple woes for a lucrative deal to coach the Seahawks.
The Seahawks gave Carroll added responsibilities equivalent to a vice president of football operations. Carroll will work alongside whomever Seattle eventually names as its new general manager on operations beyond coaching the 53-man roster.
"If you know anything about me, you know I can't pass up this challenge," Carroll said.
The Seahawks were to formally introduce Carroll at their headquarters in Renton, Wash., on Tuesday at 1 p.m. ET.
USC quarterback Matt Barkley also said quarterbacks coach Jeremy Bates is leaving with Carroll after just one season.
The Chicago Bears have been informed that Bates, who was scheduled to interview for their offensive coordinator's job, has decided to accept the same job with Carroll and the Seahawks, two sources told ESPN senior NFL analyst Chris Mortensen on Sunday night.
A source said Bates was tempted to be reunited with Bears quarterback Jay Cutler, but the long-term security with Carroll was a major factor in his decision to join the Seahawks rather than the Bears. Bates was Cutler's offensive coordinator with the Broncos in 2008.
The Bears' options for the position now include Mike Martz, Jedd Fisch and Bill Musgrave, league sources told ESPN NFL Insider Adam Schefter.
A source close to USC linebackers coach Ken Norton Jr. confirmed to ESPN's Shelley Smith that Carroll will be taking Norton to Seattle to fill the same role with the Seahawks.
Norton recruited Lakewood (Calif.) High School quarterback Jesse Scroggins, who has already committed to USC but is said to be waiting to see what happens with Carroll.
Carroll won 97 games, seven Pac-10 titles and two national championships at USC, but the school is under a cloud of NCAA investigation and other scandals. Although the charismatic 58-year-old coach spoke glowingly of his highly successful years in Los Angeles, he jumped at the best -- and timeliest -- of many offers he's received over the years to return to the NFL.
"I do not expect to ever be able to top what we just did," Carroll said. "I think it's just been a beautiful time together. It hurts to separate right now ... but it can't keep on going, because I can't pass up this opportunity."
Carroll's departure ends one of the most successful runs in college football history -- perhaps right when it was about to become much less fun, considering the just-completed 9-4 season, USC's worst since his first year at the school.
"Every Trojan everywhere owes Pete a big debt of gratitude for what he did for USC and USC football this past nine years," USC president Steven B. Sample said in a statement. "Two national championships, three Heisman Trophy winners, and seven consecutive Pac-10 championships earned him a lasting place in our history."
Carroll insisted his decision had nothing to do with the NCAA's lengthy look into his program, denouncing rumors of a rift between him and athletic director Mike Garrett. Carroll said he thought he would be at USC "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.
He's taking along Bates, who replaced Steve Sarkisian last year. Sarkisian recruited Barkley before jumping ship to the University of Washington last year.
"It's kind of disappointing to see them leave," Barkley said. "More than anything, it's a challenge to get better and just reach another level. I came to this school because I wanted to be a Trojan, and nothing about coaches leaving would change that for me."
Trojans receiver Brice Butler said it was Carroll's call to make.
"[Carroll] doesn't have to apologize," Butler said. "He made the decision that was best for him. You can't cry like a baby. Crying doesn't get you anywhere."
Schefter first reported Saturday morning the Seahawks and Carroll had reached an agreement in principle.
Next up for Leiweke is to hire a general manager.
The Seahawks have at least four interviews to conduct to find the general manager who will work with Carroll. Former Titans GM Floyd Reese is scheduled to interview, along with Giants personnel man Marc Ross, Packers executive John Schneider and Omar Khan, a contract administrator with Pittsburgh.
Seattle forced out general manager and president Tim Ruskell on Dec. 3.
Garrett brushed past dozens of reporters after Carroll's news conference, maintaining his largely silent public stance about his troubled department, which sanctioned its own men's basketball program recently in an attempt to assuage the NCAA.
"I'm working on the next step, and when I finish, you'll hear about it," Garrett said. "I don't talk about my search."
Garrett's search for a replacement is likely to be speedy, with national signing day looming Feb. 3 and several recruits already wondering about their tentative commitments to USC. Barkley and tailback Allen Bradford said they planned to be on the phone with every recruit, encouraging them to stick with the Trojans.
Oregon State's Mike Riley fell off the list of possible successors when it was announced Sunday night that he had signed a three-year extension through at least 2019.
Instead, Riley, who was a finalist for the Trojans' job in 2000, will stay in his hometown.
"Due to the fact there is a lot of speculation on my future, I want to make it known that I'm very excited to be coaching at Oregon State University and I anticipate doing so for a long time," Riley said in a statement released by the school.
Sources close to Riley said he was intrigued by the USC job, but loved coaching in Corvallis and the idea that he could finish his career there.
Tennessee Titans coach Jeff Fisher is a former USC player and California native, but previously said he wasn't interested.
Jacksonville Jaguars coach Jack Del Rio, another former USC star with no college coaching experience, might be the most interested target for Garrett, though Jaguars owner Wayne Weaver is thought to want Del Rio back for an eighth season. Weaver and Del Rio are expected to meet Tuesday.
Carroll's players were disappointed by the news. The group that straggled into Heritage Hall for an afternoon meeting chose USC largely on the strength of Carroll's success and charisma, but returned to classes Monday with no idea what was next.
"I kind of didn't want to come to the meeting today, but it's something you've got to do," said Bradford, who will be the Trojans' top returning rusher with Joe McKnight's early departure for the NFL. "How he got us training and competing, I don't think that's ever going to leave us. The new coach coming in is going to see this team is hungry and wants to win."
Bradford planned to hold a players-only meeting in the locker room after Carroll's farewell address.
"Well, I'm not surprised," junior running back Marc Tyler told ESPNLosAngeles.com's Ramona Shelburne. "I think by now most guys wanted it to hurry up and happen so we can see who is going to coach us next."
Sophomore defensive end Malik Jackson said while he was a little surprised, he understands why Carroll is leaving.
"I can't believe we're one of those teams looking for a new coach," Jackson told Shelburne. "I'd heard about it all weekend, but I'm still kind of surprised.
"I don't blame him though. We all have to make decisions in our lives. If I could've said something that'd make him come back, I would've. But I'm not mad at him. He has to do what he thinks is best for himself. Everybody does."
The USC program, meanwhile, is now leaderless at a difficult time. The school has been under NCAA scrutiny for several years as the organization investigates allegations former Trojans tailback Reggie Bush received improper benefits from a marketing agent.
Another potential NCAA problem arose last month when McKnight was forced to sit out the Emerald Bowl while the school investigated his use of an SUV that was not registered to him.
McKnight, along with star wide receiver Damian Williams, declared for the NFL draft as juniors last week.
Information from ESPN NFL Insider Adam Schefter, ESPN's Shelley Smith, ESPNLosAngeles.com's Ramona Shelburne and The Associated Press was used in this report.