He says he wants to spend more time with his children and dedicate himself even more to the fight against cancer with his "Livestrong" Foundation.
It's been nearly a month since he finished 65th in his last competitive race in Australia. Having retired from the sport in 2005 after winning a record seventh Tour de France title, the cancer survivor came back to compete in the 2009 Tour. Armstrong was unable to reach the heady heights of his peak years though and finished behind Alberto Contador and Andy Schleck - a situation he had not expected.
Armstrong will miss competing - let alone dominating a sport like none before him - but not the gruelling training regimen that made it possible.
"I can't say I have any regrets. It's been an excellent ride. I really thought I was going to win another tour," Armstrong said about his comeback attempt in 2009. "Then I lined up like everybody else and wound up third.
"I have no regrets about last year, either," he added, despite finishing 23rd. "The crashes, the problems with the bike - those were things that were beyond my control."
He ends his career in the shadow of a federal doping investigation. He has denied allegations from former teammate Floyd Landis that he used performance-enhancing drugs.
The Associated Press contributed to this report.