"I started in cold gyms in small towns in Iowa and ended up playing in more than 1,000 games over 15 years in the best league in the world," Collison told ESPN's Royce Young. "I've had an incredible run. I'm proud of my career.
"But it's time to go. I'm retiring from competitive basketball."
After four years playing for Roy Williams at Kansas, including two Final Four appearances, Collison was selected 12th overall by the Seattle SuperSonics in the illustrious 2003 NBA Draft and remained with the franchise as it moved to Oklahoma in 2008. Kevin Durant and Jeff Green are now the only two active players who have played in Seattle.
"I learned an important lesson: The NBA is a business and all the parties involved will always act in their own best interests," Collison said. "The fans in Seattle deserved better, and I hope they get a team back someday soon."
Collison missed the entire 2003-04 season with a dislocated shoulder he suffered in training camp, and debuted in November of the following season. He played his first four years with the SuperSonics.
In 2012, Collison made his lone trip to the NBA Finals on a Thunder team that featured Durant, Russell Westbrook, and James Harden. LeBron James and the Miami Heat defeated them in five games, and Collison's trio of superstar teammates was broken up when Harden was subsequently dealt to the Houston Rockets. Durant left Oklahoma a few seasons later to join the Golden State Warriors.
"I love (Kevin Durant). I miss him," Collison said. "I played my best basketball with James. I wish we would have had more time. I feel like a proud big brother watching Russ become both the player and the man that he is. I really appreciate all the battles we've been through."
Collison averaged 5.9 points and 5.2 boards in 910 career games. His peak statistical season was 2007-08 - his finale in Seattle - where he averaged 9.8 points and 9.4 boards in 78 contests.