"We are pleased to announce that Nick will remain a core member of our organization," Blackhawks vice president and general manager Stan Bowman said in a statement. "Over the course of the past three seasons, Nick has shown continuous development and we think he will be essential to our long-term success."
Leddy, 22, would have become a restricted free agent Friday.
The Blackhawks acquired Leddy on Feb. 12, 2010, from the Minnesota Wild, who had taken him with the 16th pick in the 2009 NHL Draft. He played in all 48 regular-season games for Chicago in 2012-13, scoring six goals and finishing with 18 points and a plus-15 rating.
Leddy also played in all 23 of Chicago's games during the Stanley Cup Playoffs, with two assists and a minus-8 rating. He saw a total of 12:55 of ice time during the last three games of the Stanley Cup Final against the Boston Bruins.
"I'm thrilled to have the opportunity to remain in Chicago and be a part of this special group of young, experienced players on a team in a winning environment," Leddy said in a statement. "The organization is first-class both on and off the ice, and I am honored to be a member of the Chicago Blackhawks."
The 6-foot, 191-pound native of Eden Prairie, Minn., has 13 goals and 62 points in 176 regular-season NHL games, all with Chicago.