Armstrong's day started with an apology to his Livestrong Foundation staff and ended with a lengthy interview with Winfrey. A person close to Armstrong says his interview was "emotional at times."
Early Monday morning, local and international media gathered outside of Armstrong's home in Austin, Texas, where the interview was originally set to take place. But the venue changed to a hotel in downtown Austin, where Armstrong was joined by about 10 close friends and advisers.
Specifics of what Armstrong said are being kept under wraps for now, but a person close to the situation says he did confess to using performance-enhancing drugs.
The interview on the Oprah Winfrey Network is set to air Thursday night. Shortly after the interview, Winfrey tweeted "Just wrapped with @lancearmstrong More than 2 1/2 hours . He came READY!"
Armstrong was stripped of his seven Tour de France titles last year because of doping charges and running what officials called a sophisticated doping operation.
Prior to meeting with Winfrey, he gathered about 100 staffers with his Livestrong Foundation to personally apologize. A spokeswoman for Livestrong said Armstrong "took responsibility" for the trouble he caused the foundation. She also described his apology as "sincere and heartfelt," and that Armstrong choked up while several employees cried.
Another person with direct knowledge of the meeting said Armstrong did not make a direct confession to them, but said he would try to restore the foundation's reputation.
ABC News has learned that a very high-level source says Armstrong is now talking with authorities about paying back some of the U.S. Postal Service money from sponsoring his team. He is also talking to authorities about naming names and confessing, even giving up others involved in illegal doping. This could possibly result in a reduction of his lifetime ban.
The Associated Press contributed to this report.