Hjalmarsson's deal will keep the 26-year-old Swede with Chicago through the 2018-19 season.
The team didn't disclose financial terms, but Canadian broadcaster TSN reported the contract was worth $4.1 million annually.
The blueliner has played a key role in each of the Blackhawks' Stanley Cup championships in 2010 and this past season, during which he had five assists and a plus-10 rating in 23 post-season games.
A fourth-round 2005 draft pick by Chicago, Hjalmarsson played all 48 games of the lockout-shortened 2012-13 season, providing two goals with a career-best plus-15 rating.
He sports a plus-48 rating with nine goals and 47 assists over 306 career regular season games.
The Blackhawks on Monday also signed goaltender Corey Crawford to a six-year deal.