In an interview with CNN, the cycling legend - who was stripped of his seven Tour de France titles after admitting years of doping - said that it was only the US Anti-Doping Agency's dogged investigation which forced his hand.
"Once you say 'no' you have to keep saying 'no'," he said.
"If this stuff hadn't taken place with the federal investigation, I'd probably still be saying 'no' with the same conviction and tone as before. But that gig is up."
Armstrong is planning a book in which he will tell the entire sordid history of his years of cheating - from the drugs themselves to the lengths he went to in order to cover his tracks and discredit those who tried to blow the whistle.
"There has to be totally no bull****," he said of his new tome, which is expected to become as big a best-seller as his now-infamous autobiography It's not about the bike.
"I'm fully committed to putting it all out there. I don't blame anyone for thinking, 'I don't trust this guy with all his bull**** for 10 years'...
"The book needs to be pretty intense and transparent. I need to 'boom' -- put it out there and let it sit.
"The sooner the better. It has to be the right book, the right tone and there has to be totally no bull****."
He added that he will not try and deflect any blame.
"I'm a big boy, I made my own decisions and I need to be held accountable for that," he said.
"I'm not going to blame people. A lot of people have blamed everyone else but that's bull****.
"No-one forced me or bullied me, so I'm not going to say, 'It's not my fault.' I blame myself, that's the bottom line."
Armsong said that his life is still good despite his shame, with the only vitriol directed at him coming via the internet.
"In this day and age, there's plenty of outlets for people to hurl the most heinous comments that you can think of, you only have to look at the comments that will be at the bottom of this piece," the 42-year-old said.
"But day-to-day life is positive. I never get crap, not once, and I'm surprised by that. Sure, I sometimes get the vibe that someone wants to say something, but it's never happened."