The four-time Finnish Olympic medalist and cancer survivor announced his decision through the NHL players' association. The Ducks decided they wouldn't attempt to re-sign Koivu earlier in the summer.
The 39-year-old Koivu spent his first 13 NHL seasons with Montreal, becoming the first European-born captain in the Original Six franchise's history in 1999. He signed with the Ducks in 2009, playing five seasons on the West Coast before joining longtime friend Teemu Selanne in retirement.
"All in all, it has been a dream come true," Koivu said in a statement released by the NHLPA. "But what I value the most in hockey is the feeling of being part of a team and the friendships I have made along the way. ... I have been contemplating retirement for quite some time, and am very confident in my decision at this time and place."
Koivu missed nearly the entire 2001-02 season while undergoing treatment for non-Hodgkin lymphoma. He recovered in time to play in the final three games of the regular season, helping Montreal to make the playoffs.
Koivu won the Bill Masterton Trophy in 2002 for perseverance, sportsmanship and dedication to hockey. He also won the King Clancy Trophy for leadership and humanitarian work in 2007.
He was the Canadiens' captain from 1999 to 2009, tying Jean Beliveau as the longest-serving captain in Montreal history. While never a goal-scoring star, Koivu twice was voted to the NHL All-Star game in recognition of his dependable two-way game.
"My time in Montreal was special beyond playing hockey," Koivu said. "Thank you to the fans and lovely people of Montreal for your support and love, and for providing my family and me with wonderful memories that we will always cherish, as well as the immense support during my illness."
After joining the Ducks as a free agent in 2009, Koivu frequently teamed up on a line with Selanne, his fellow fan favorite in Anaheim.
He cracked the Ducks' franchise top 10 in goals and assists while scoring 191 points in 332 games with Anaheim, but Koivu occasionally struggled with injuries as his scoring production dropped over the past two seasons. Anaheim general manager Bob Murray announced in June that the club wouldn't offer him another contract.
"He was a great attribute to us," Ducks coach Bruce Boudreau said Wednesday. "He's a great human being, and everything he did was well-deserved. I want to congratulate him and thank him for the years."
Koivu had 255 goals and 577 assists in 1,124 career NHL games, but never advanced past the second round of the playoffs. He scored a career-high 75 points for Montreal during the 2006-07 season.
Koivu also served as Finland's team captain for each of his four Olympic trips and several additional international competitions.
Along with three Olympic bronze medals, he earned silver in 2006 after Finland lost to Sweden in the final in Turin. Koivu didn't play for Finland in Sochi this year to preserve his health for the Ducks' season, which ended with a painful seven-game loss in the second round to the eventual Stanley Cup champion Los Angeles Kings.
Koivu previously said he plans to keep living in Irvine, California, with his wife and two children after retirement.
"Orange County has truly been a blessing for us," Koivu said.
Koivu's younger brother, Mikko, is the captain of the Minnesota Wild.