The dramatic seventh game of what had been a thrilling series appeared to have been decided late in the third period when Chicago's Niklas Hjalmarsson scored to seemingly put the Blackhawks in front.
Behind the play, however, coincidental penalties were called on Chicago's Brandon Saad and Detroit's Kyle Quincey. That led to Hjalmarsson's goal being negated and that controversial call could have been one that cost the Blackhawks.
Chicago, however, prevailed when Seabrook broke in by himself and launched a shot that deflected off the left shoulder of Detroit defenseman Niklas Kromwall. That slight change of direction sent the puck past Howard and touched off the Blackhawks' celebration.
Seabrook collected the puck when it came loose in the neutral zone following a hit by Chicago's Dave Bolland on Gustav Nyquist along the boards.
The Blackhawks, who finished the regular season with the best record in the NHL, will play in the Western Conference finals against the defending Stanley Cup champion Los Angeles Kings. That series will open Saturday in Chicago.
The Eastern Conference finals will be contested between the Pittsburgh Penguins and Boston Bruins.
Corey Crawford made 26 saves to get the victory, improving to 8-4 in this year's playoffs. Howard stopped 33 shots.