Leddy received a deal worth $5.4 million, a source told ESPN.com's Pierre LeBrun.
The 22-year-old Leddy, who became a restricted free agent after this past season, has played the past three seasons with the Blackhawks.
"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."
Leddy had six goals, 12 assists and a plus-15 rating in 48 regular-season games last season. He had zero goals, two assists and a minus-8 rating in 23 playoff games. His minutes were reduced throughout the playoffs, and he saw a career-low 2:37 of ice time in Game 4 of the Stanley Cup finals against the Boston Bruins.
Despite Leddy's decreased role in the playoffs, Blackhawks general manager Stan Bowman recently spoke positively of the defenseman and said he was in the organization's future plans.
"I think it's a great experience for Nick, and I'll tell you, when you look back at Game 6 [of the Stanley Cup finals], I'm really proud of the way Nick responded there," Bowman said on June 27. "He hadn't played in a while and he jumped out while we were down and he had a couple great shifts there. He kind of got the momentum going and then I think it was the next shift is when we tied the game. So, he played a big part in it.
"I know he didn't get a lot of minutes, but that's not easy to do, to come off the bench when you haven't played. So, we're excited about his future. He's taken steps every year and I expect next year to be another one where he's going to raise his game. He's got that experience now of having won a Cup and being a big part of it, so I look forward to next year for him."
Since winning the Stanley Cup, the Blackhawks have re-signed Leddy and forward Bryan Bickell while trading forwards Dave Bolland (to the Toronto Maple Leafs) and Michael Frolik (Winnipeg Jets), both for draft picks.
The Blackhawks also are negotiating with restricted free agent Marcus Kruger, according to Kruger's agent.
Information from ESPN.com's Pierre LeBrun was used in this report.