Armstrong on Thursday night dropped any further challenges to USADA's allegations that he took performance-enhancing drugs to win cycling's premier event from 1999-2005.
In a news release, USADA said Armstrong's decision not to take the charges against him to arbitration triggers the lifetime ineligibility and forfeiture of all results from Aug. 1, 1998, through the present. The agency said it expected cycling's governing body to take similar action, but the International Cycling Union (UCI) was measured in its response, saying it first wanted a full explanation on why Armstrong should relinquish his Tour titles.
The Amaury Sport Organization that runs the world's most prestigious cycling race said it would not comment until hearing from the UCI and USADA
Armstrong, who retired last year, said he was weary of fighting accusations that have dogged him for years. He has consistently pointed to the hundreds of drug tests that he has passed as proof of his innocence. He contends USADA was on a "witch hunt."
Still to be heard from was the sport's governing body, the International Cycling Union, which had backed Armstrong's legal challenge to USADA's authority.
Armstrong has been battling doping allegations ever since he won his first Tour in 1999. In recent years, former teammates have come forward to claim Armstrong not only doped, but led the cover-up of a doping ring that involved several other riders.
The USADA says Armstrong not only doped himself, but also ran a complex doping ring that involved many of his teammates.
Included in USADA's evidence were emails written by Armstrong's former U.S. Postal Service teammate Floyd Landis, who was stripped of his 2006 Tour de France title after a positive drug test. Landis' emails to a USA Cycling official detailed allegations of a complex doping program on the team.
USADA also said it had 10 former Armstrong teammates ready to testify against him. Other than suggesting they include Landis and Tyler Hamilton, both of whom have admitted to doping offenses, the agency has refused to say who they are or specifically what they would say.
Armstrong sued USADA in Austin, where he lives, in an attempt to block the case and was supported by the UCI, the sport's governing body. A judge threw out the case on Monday, siding with USADA despite questioning the agency's pursuit of Armstrong in his retirement.
"USADA's conduct raises serious questions about whether its real interest in charging Armstrong is to combat doping, or if it is acting according to less noble motives," such as politics or publicity, U.S. District Judge Sam Sparks wrote.
Armstrong's victories made him one of the biggest stars in the world, and a hero to many because he came back to dominate his sport after beating cancer. But he said this fight had exhausted him and his family.
"There comes a point in every man's life when he has to say, 'Enough is enough.' That time is now," he said in a statement.
Armstrong could have pressed his innocence in USADA's arbitration process, but the cyclist has said he believes most people have already made up their minds about whether he's a fraud or a persecuted hero.
"I'm sick of this," Armstrong said in 2005. "Sitting here today, dealing with all this stuff again, knowing if I were to go back, there's no way I could get a fair shake - on the roadside, in doping control, or the labs."
The Associated Press contributed to this report.