United States Attorney AndrDe Birotte Jr. announced in a press release that his office "is closing an investigation into allegations of federal criminal conduct by members and associates of a professional bicycle racing team owned in part by Lance Armstrong."
He did not disclose the reason for the decision.
Armstrong has repeatedly denied doping during his unparalleled career, but the possibility of criminal charges threatened to stain his legacy as the world's greatest cyclist and could have cast a shadow over his cancer charity work.
The investigation picked up steam after cyclist Floyd Landis, winner of the 2006 Tour de France, was stripped of the title after testing positive for drug use. After years of denial, Landis admitted in 2010 that he cheated. During an interview with ABC News, he said Armstrong also used illegal substances.
Armstrong consciously maintained a high profile throughout the investigation, raising money for his cancer charity, Livestrong, and racing in events such as off-road triathlons. He had no reason to hide, he said.
Armstrong released a statement saying, "I look forward to continuing my life as a father, a competitor and an advocate in the fight against cancer without this distraction."
Armstrong won the Tour de France every year from 1999-2005.
The Associated Press contributed to this report.