Seabrook has built a reputation as a clutch player in the postseason.

He scored in overtime in Game 7 of the second round of the 2013 Stanley Cup Playoffs as the Chicago Blackhawks rallied from a 3-1 series deficit to eliminate the Detroit Red Wings on the way to the title. He also scored in OT in Game 4 of the Cup Final against the Boston Bruins that spring. Seabrook scored his third playoff OT winner April 21, 2015, against the Nashville Predators, in another Cup-winning spring for the Blackhawks.

Before his NHL success, Seabrook played in the Western Hockey League with Lethbridge from 2000-05 and helped Canada win the 2003 World Under-18 Championship. He was selected by the Blackhawks in the first round (No. 14) of the 2003 NHL Draft.;

Seabrook played for Canada at the World Junior Championship in 2004 and 2005, winning a gold medal in 2005, and made his pro debut in 2004-05 with Norfolk of the American Hockey League. He had an assist in his NHL debut for Chicago against the Anaheim Ducks on Oct. 5, 2005, then had four assists in his second NHL game two days later against the San Jose Sharks, matching a franchise single-game record for points and assists by a rookie. Seabrook scored his first NHL goal Nov. 2, 2005, in overtime against the St. Louis Blues and played for Canada at the 2006 World Championship.

Seabrook played in the YoungStars Game as part of the 2007 NHL All-Star Game festivities. Among Blackhawks defensemen in 2007-08, he was first in assists (23) and tied for the lead in points (32). He led Chicago in hits (224) and blocked shots (113) in 2008-09.

Seabrook got his first playoff point with an assist on April 18, 2009, and his first NHL playoff goal April 25, 2009, each coming against the Calgary Flames. He led the Blackhawks with 153 blocked shots in 2009-10, then had four goals and seven assists in 22 playoff games to help Chicago win the Stanley Cup that year (he had seven points in four games from April 24-May 3, 2010). Seabrook also won a gold medal with Canada at the 2010 Winter Olympics.

He was one of seven NHL defensemen to have more than 100 hits (106) and blocked shots (103) in 2012-13 as Chicago again won the Stanley Cup. Seabrook shared the team lead among defensemen with seven goals in 2013-14. His 31 points in 2014-15 included a seven-game point streak from Nov. 14-28, 2014. He scored seven goals in 23 playoff games in 2015, a franchise record, and won his third Stanley Cup with Chicago.

On Dec. 27, 2015, Seabrook became the fifth defenseman in franchise history to reach 800 games played.