It will be a yearly $5.8 million cap hit, a source told ESPN.com.
"The Blackhawks are the only organization I've ever played for, and I've been a part of something very special in Chicago over the last six seasons," said Seabrook. "I'm excited to continue being a part of this group, playing in the United Center and making our fans proud."
Seabrook will make $7 million in both 2011-12 and 2012-13, comprised of a $5 million salary and $2 million signing bonus, according to the source. He will then make $5 million a season from 2013-16, according to the source.
Seabrook, 25, was in the last year of a three-year deal and was to be a restricted free agent at the season's end.
"We're getting close to where you want to get it done or set it aside," Blackhawks vice president/general manager Stan Bowman said. "We both realized it had gotten to that point and motivated both of us to really get it finished."
Bowman said the two sides started working on a deal in October.
"We knew all along we wanted to sign Brent, and he was a big part of what we've accomplished here," Bowman said. "It took a little bit longer than I guess we both wanted but these things do. Just happy that it got done."
Last season, Seabrook helped the Blackhawks win their first Stanley Cup title in 49 years. He also was on the Canadian team that won the gold medal at the 2010 Vancouver Olympics.
Seabrook has four goals and 29 assists and a plus-2 rating this season for the Blackhawks.
"He's been a fixture on our defense," Bowman said. "He came up as a 20-year-old kid. He didn't spend any time in the minor leagues. He came in right away and made our team. He's been an NHL player ever since. Each year he's been getting better. I'm not sure he's reached his potential. That factored into it."
Information from ESPN.com's Pierre LeBrun and ESPNChicago.com's Jesse Rogers was used in this report.