The deals came less than 24 hours after the Coyotes and coach Dave Tippett mutually agreed to part ways. It comes less than a week after captain Shane Doan, an unrestricted free agent on July 1, was told he would not be returning for the 2017-18 season.
RELATED: [Stepan, Raanta traded to Coyotes by Rangers | Hjalmarsson traded to Coyotes by Blackhawks\]
As a result, the need for some veteran presence became much more acute.
"We need winners," Coyotes GM John Chayka said. "We have a lot of great young players; we need some leaders and some guys to show them how it is done."
Hjalmarsson, 30, who was obtained for defenseman Connor Murphy and center Laurent Dauphin, has won three Stanley Cups with the Chicago Blackhawks in his 10-year NHL career.
He will join Oliver Ekman-Larsson on the top pair. They have played together in the past for the Swedish national team.
Ekman-Larsson, the new face of the franchise after the departure of Doan, struggled this season, with 39 points (12 goals, 27 assists), a nine-goal and 16-point downturn from 2015-16.
"Oliver, I think what makes him special, is playing with the puck and his offensive side of the game, the way he makes plays," Chayka said. "Hjalmarsson is an elite defender, one of the best, and he kind of covers up and frees Oliver up to do his thing. Obviously they are good friends and I think there is a lot of synergy there."
Also in the mix is defenseman Pierre-Olivier Joseph, who the Coyotes selected in the first round (No. 23) on Friday. Joseph (6-2, 163) had 39 points (six goals, 33 assists) in 62 games with Charlottetown of the Quebec Major Junior Hockey League.
As for Stepan, he is the No. 1 center the franchise has sought, without success, for the past decade. The cost was Arizona's first-round pick, No. 7, in the NHL Draft on Friday and defenseman Tony DeAngelo, a first-round pick in 2014 by the Tampa Bay Lightning.