Carroll's previous deal was due to expire after the 2014 campaign, but the Seahawks have now tied him down until 2016 after he led the franchise to their first ever Super Bowl success last season.
The 62-year-old is 38-26 in his four seasons with Seattle so far, and general manager John Schneider was delighted to have sealed a deal to prolong Carroll's stay.
"This was a huge priority for us coming into the offseason," Schneider told The AP.
"We knew it was around the corner, and quite honestly we're trying to take care of our own people and keep our young players together. But where do you start? You start at the top."
The Seahawks finished the 2013 regular season with a 13-3 record before beating the New Orleans Saints, San Francisco 49ers and nullifying the record-breaking offence of the Denver Broncos to win the Super Bowl.