The 41-year-old released a statement saying he was "finished with this nonsense" and insisted he is innocent, but did not want to spend any further effort clearing his name.
He said: "There comes a point in every man's life when he has to say, 'Enough is enough'. For me, that time is now.
"I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999."
Armstrong faces having his unprecedented run of Tour wins stripped out of the record books, as well as a lifetime ban from any sport signed up to the World Anti-Doping Agency code.
His decision to walk away from the charges against him casts a cloud of doubt over proceedings.
The USADA have treated his move as an admission of guilt, but it is a guilt that has not been proven by arbitration hearings where the evidence against him has been judged on its merits.
WADA chief John Fahey believes Armstrong's decision not to fight the charges meant there was 'substance' to those allegations.
"He had the right to rip up those charges but he elected not to, therefore the only interpretation in these circumstances is that there was substance in those charges," Fahey said.
"My understanding is that when the evidence is based upon a career that included seven Tour de France wins then all of that becomes obliterated."
The USADA also accused five of Armstrong's associates including Johan Bruyneel, the sporting director who guided the American to his Tour triumphs.
Proceedings against them are ongoing but Tygart told velonation.com the evidence, believed to include testimony from up to 10 of Armstrong's former team-mates, will be released "in due course".
When asked if he expected details of the evidence against Armstrong to emerge, he said: "Yes, absolutely...at the right time.
"Obviously there are other cases that are alleged to be involved in the conspiracy. Their cases are still proceeding, so it will be in due course."
When asked if there was any impediment to the USADA releasing those details, he replied: "No."
Tygart also insisted the USADA have the power to strip Armstrong of his Tour titles.
Cycling's international governing body, the UCI, have contended they should have jurisdiction over Armstrong's case as they were responsible for carrying out doping tests while he competed.
Armstrong has been at pains to point out that he has never failed a drug test.
The UCI could choose to appeal to CAS against the USADA ruling, or to gain jurisdiction over the case.
But Tygart is confident his body have the power to hand down their sanctions.
He said: "They (Armstrong and his legal team) have already taken legal action and the federal judge told them we do have authority and our process is the process where those complaints can be made.
"It is kind of funny that they walking away from a process, but are threatening to attempt to go back to somewhere else to fight. It is a little ironic but, no...it means nothing."
The UCI have released a statement saying they will wait to receive a required communication from USADA explaining its actions before making further comment.
It read: "The UCI notes Lance Armstrong's decision not to proceed to arbitration in the case that USADA has brought against him.
"The UCI recognises that USADA is reported as saying that it will strip Mr. Armstrong of all results from 1998 onwards in addition to imposing a lifetime ban from participating in any sport which recognises the World Anti-Doping Code.
"Article 8.3 of the WADC states that where no hearing occurs the Anti-Doping Organisation with results management responsibility shall submit to the parties concerned (Mr Armstrong, WADA and UCI) a reasoned decision explaining the action taken.
"As USADA has claimed jurisdiction in the case the UCI expects that it will issue a reasoned decision in accordance with Article 8.3 of the Code.
"Until such time as USADA delivers this decision the UCI has no further comment to make."
