The former Tour de France champion was stripped of his several titles last year when an investigation by the United States Anti-Doping Agency concluded that the athlete had used performance enhancing drugs.
Armstrong denied the allegations vehemently, but declared that he would not appeal the USADA's decision to ban him from competitions in the interest of his family.
Reports that the 41-year-old was ready for a possible admission came out earlier this month when it was revealed that he would be interviewed for an episode of Oprah's Next Chapter.
A source close to the production has now told The AP that Armstrong did confess to doping during the interview, which took place at a Texas hotel not far from the headquarters of his Livestrong organisation.
Winfrey tweeted after the interview: "Just wrapped with [Lance Armstrong]. More than 2 1/2 hours. He came READY!"
Armstrong's episode of Oprah's Next Chapter airs Thursday, January 17 at 9pm on OWN in the US.
> Lance Armstrong 'apologises to Livestrong Foundation staff'
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