Hossa, who surprisingly took a one-year deal with the defending champion Red Wings last summer, cashed in this time.
The four-time All-Star and 11-year NHL veteran has played on the Stanley Cup runner-up the last two seasons -- while with the Penguins he lost to the Red Wings and this year with Detroit, he fell to Pittsburgh in the rematch.
The young Blackhawks are his fourth team since 2008.
"Now I don't have to worry about dealing with it year-to-year. I'm set for 12 years. That will make it easier and I can focus on hockey," Hossa said.
Chicago also signed center Tomas Kopecky, who, like Hossa, played last season with the Red Wings. He was knocked out of the playoffs after sustained injuries to his face during a fight with Anaheim Ducks defenseman Francois Beauchemin in the second round.
By adding Hossa, the Blackhawks won't be re-signing Martin Havlat, who led the team in points last season. A free agent, Havlat made $6 million last season at the end of a three-year deal. The Blackhawks also did not re-sign goaltender Nikolai Khabibulin, their starter during the playoffs last season, who earned a new deal with the Edmonton Oilers on Wednesday.
"We were just unable to get a deal done with Marty," general manager Dale Tallon said. "It was 11:01 and we decided to go in a different direction. The important thing we're doing is to keep the core together. So this deal was important to get done at this term to help us in the future solidify that core group. ... I wish Marty and Nik all the best. We're turning the page and moving forward."
The 30-year-old Hossa will also be counted on for some leadership. The Blackhawks, who lost to the Red Wings in the Western Conference finals in May, were the youngest team in the NHL last season.
"Marian has played a lot of games," Tallon said. "The most-important thing for Marian is that he wants to win and he feels we're headed in the right direction and that he can be as a 30-year-old one of our elderly statesmen on our team and help lead this young team."
Hossa has played for Ottawa (1997-2004), Atlanta (2005-08), Pittsburgh (2008) and Detroit (2008-09), recording 719 points -- 339 goals and 380 assists -- in 775 regular-season games. He has appeared in 98 playoff games with 31 goals and 45 assists.
"I will be one of the oldest guys, which will be strange for me, a little different, but I'm looking forward to playing with a young team," Hossa said during a conference call.
He led the Red Wings with 40 goals last season and was third on the team with 71 points. He had 15 points -- six goals and nine assists -- in the playoffs where the Red Wings were dethroned in the finals by the Penguins. He had no goals and three assists in the seven games against Pittsburgh.
"I had a great time in Detroit. ... But with today's economy and the salary cap, it's really hard to sign star players," Hossa said.
"Somebody just couldn't be able to sign and I guess that was me," he added. "That was basically a great year. It didn't finish how I would like. Now it is time to move on. I was hoping to sign a long-term deal and Chicago made a great offer."
Hossa was chosen by Ottawa in the first round of the 1997 draft.
Kopecky had 109 hits, six goals and 13 assists in 79 games for the Red Wings last season, his fourth with Detroit.
The Blackhawks believe Hossa is the difference maker that get them to the finals and bring a Stanley Cup back to Chicago for the first time since 1961.
"He's a horse out there. He can play defense and offense and score 40 goals. He's a hard guy to slow down and to stop. He's durable," Tallon said.
"He's a game-breaker."