Hjalmarsson was drafted 108th overall in the 2005 NHL Entry Draft by the Chicago Blackhawks. He played professionally for three years in the Elitserien with HV71. In the 2007–08 season, his first in North America, Hjalmarsson made his NHL debut with the Blackhawks. After spending the majority of the season with the Rockford IceHogs, Chicago's American Hockey League affiliate, he procured a regular spot on the roster after defenceman James Wisniewski's trade to the Anaheim Ducks. Hjalmarsson scored his first career NHL goal against Chris Osgood of the Detroit Red Wings. Hjalmarsson became a key part of the Blackhawks' lineup late into the 2008–09 season and to begin the 2009–10 season. In 2009–10, he played 77 games in the regular season and all 22 in the Stanley Cup playoffs for the team, averaging over 19 minutes played per game, switching between the second and third defensive pairings. Over that time, he recorded a production value of a point roughly every 45 minutes of it, while his season PROD was 89 minutes. During the 2010 Stanley Cup playoffs, a slapshot Hjalmarsson took was redirected by teammate Andrew Ladd to give Chicago a 3–2 lead in Game 6 of the Stanley Cup Finals; the team won the game in overtime, 4–3, and eventually the 2010 Stanley Cup. to Eksjö, Sweden, after the Blackhawks won the 2010 Stanley Cup Finals On 9 July 2010, shortly after the end of the season, Hjalmarsson signed a four-year, $14 million offer sheet with the San Jose Sharks. Three days later, however, on 12 July, the Blackhawks announced that they would match the offer sheet. Hjalmarsson became the first NHL defenceman in 13 years to receive an offer sheet as a restricted free agent, and, critically, Chicago's matching of the offer meant that they no longer had enough cap space to re-sign goaltender Antti Niemi, who coincidentally ended up joining the Sharks later that off-season. During 2012–13 NHL lockout, Hjalmarsson played in the Italian Serie A and in the IIHF Continental Cup with HC Bolzano. During game 7 of the western conferences semifinals against the Detroit Red Wings, with the score tied at 1-1 late in the third period, Hjalmarrson scored what appeared to be a go ahead goal with 1:47 left in regulation time, but referee Stephen Walkom called offsetting penalties on Detroit's Kyle Quincey and Chicago's Brandon Saad just before the puck went in, so the goal was disallowed. Brent Seabrook went on to score the game winning goal in overtime, to win the series for the Blackhawks. The Chicago Blackhawks won the 2013 Stanley Cup Finals. During the 2013 off-season, Hjalmarsson signed a five-year extension with the Blackhawks, at an annual average salary of $4.1 million. The Blackhawks won the Stanley Cup again in 2015, making Hjalmarsson one of only seven players to be part of the 2010, 2013, and 2015 Stanley Cup victories.
Arizona Coyotes
After the 2016–17 season, his tenth year with the Blackhawks, Hjalmarsson's tenure with the club came to an end as he was dealt to the Arizona Coyotes in exchange for Connor Murphy and Laurent Dauphin on June 23, 2017. Hjalmarsson was named an alternate captain for the Coyotes to begin the 2017–18 season.
