Confessing his "toxic" tale to chat show host Oprah Winfrey, Armstrong described himself as a "flawed character" while at last owning up to being at the centre of one of the biggest drugs scandals in world sport.
In just one word at the beginning of the interview broadcast worldwide, cancer survivor Armstrong confirmed his place in any gallery of fallen icons who have shamed their sport, the likes of drug-cheat sprinters Ben Johnson and Marion Jones - and his admission brought outraged reactions from around the world.
"Yes," he replied when asked directly whether he had used performance-enhancing drugs.
Winfrey rapidly fired questions at him, offering the 41-year-old little respite, grilling him about every aspect of his tainted career.
Without hesitation, and showing no signs of emotion, Armstrong replied "yes" to questions about whether he used specific drugs, including erythropoietin, human growth hormone, and blood doping.
When asked why he had repeatedly lied about using banned substances until Thursday's startling admission, he told Winfrey: "I don't know I have a great answer.
"This is too late, probably for most people, and that's my fault. I view this situation as one big lie that I repeated a lot of times.
"This story is so bad...so toxic.
"It's not as if I said no and moved off it. While I've lived through this process, I know the truth. The truth isn't what I said and now it's gone."
Armstrong inspired millions with what had seemed like a fairytale career, and said he did not believe he could have achieved what he did without breaking the rules due to a culture of drugs in cycling.
"Not in that generation. I didn't invent the culture, but I didn't try to stop the culture," he said.
"It's hard to talk about the culture. I don't want to accuse anyone else. I'm here to acknowledge my mistakes.
"I will spend the rest of my life trying to win back trust and apologizing to people."
Armstrong said he had never considered himself to be a cheat and had been sure he would get away with it, until out of competition tests were introduced and testing procedures dramatically improved.
The last time he cheated was in 2005, he said, when he won his seventh Tour de France on the streets on Paris. He made a comeback in 2009 but said he never used drugs again.
"I looked up the definition of a cheat to gain an advantage. I didn't view it that way. I viewed it as a level playing field," he said.
Armstrong's admission came just months after the U.S. Anti-Doping Agency released a detailed report describing him as the ringmaster of the "most sophisticated, professionalized and successful doping program that sport has ever seen."
While he confessed to cheating and bullying, he denied several of the other accusations that have been made against him.
He rejected suggestions he failed a doping test at the 2001 Tour of Switzerland then paid off the International Cycling Union and doping officials to cover up the result.
"That story isn't true. There was no positive test, no paying off of the lab. The UCI did not make that go away. I'm no fan of the UCI," he said.
Armstrong said he thought he had got away with it when he retired for good in 2011 but his downfall was triggered by a two-year federal investigation that was dropped but led to the USADA probe.
USADA boss Travis Tygart said Armstrong still had some way to go if he wanted to make amends.
"Tonight, Lance Armstrong finally acknowledged that his cycling career was built on a powerful combination of doping and deceit," Tygart said in a statement.
"His admission that he doped throughout his career is a small step in the right direction. But if he is sincere in his desire to correct his past mistakes, he will testify under oath about the full extent of his doping activities."
Armstrong has already been banned for life, stripped of all his race wins and dumped by his sponsors but his problems are far from over.
"I thought I was out of the woods," he said. "I just assumed the stories would continue for a long time. We're sitting here because there was a two-year federal criminal investigation."
On Thursday, hours before the interview went to air, the International Olympic Committee (IOC) stripped him of the bronze medal he won at the 2000 Games.
The IOC said after the interview that Armstrong's confession was "too little, too late" and echoed Tygart's call for him to testify at an inquiry.
"What I expect, and what would be in his own interest if he is out to recover some credibility, is to face under oath an inquiry led by a team of experts," IOC vice-president Thomas Bach told Reuters.
As a result of his confession, the Texan now faces the prospect of legal challenges and orders to repay some of the millions of dollars he earned from his success.
One company, Texas-based SCA Promotions, said it would sue the fallen cyclist if he did not pay back $12 million they paid out for Tour de France wins.
"He doesn't deserve, and is not entitled to, that money," Jeff Tillotson, a lawyer for SCA Promotions told Reuters.
Legal experts said that while Armstrong was unlikely to face criminal exposure, his admission would make it more difficult to defend against civil lawsuits, including a federal whistleblower claim filed by former team mate Floyd Landis.
"There are lawyers across the country representing various interests who are recording that interview," said Matt Orwig, a former federal prosecutor now with the law firm Jones Day.
"From a legal perspective, his issues are becoming more difficult, not less."
Cycling would take a decade to recover from the Armstrong era and other doping scandals, reformed British doper David Millar said.
"There is a generation now within professional cycling who are winning the biggest races clean...but they unfortunately are tarnished by the previous generation's mistakes," Millar said in Madrid.
"It's going to take probably 10 years now of (there) being no drug scandals before people start to believe again."
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