The American, who won the race seven times before being stripped of all seven titles last year, turned down the offer.
The deal, put forward by the US Anti-Doping Association, came as they were collecting information on Armstrong’s former team-mates and would have required him to dish the dirt on his fellow offenders.
In return, the Texan would have lost only his 2004 and 2005 titles, and still been crowned Tour de France champion between 1999 and 2003, as well as receive a shortened ban.
Those who did co-operate with the investigation - 11 Armstrong team-mates did speak out – ended up receiving six-month bans from the sport.
But instead Armstrong rejected the offer, and only in 2012 was he given a lifetime ban.
USADA chief executive Travis Tygart described the moment when the offer was rejected as “one of the lowest days of our investigation. We were disappointed he wasn’t part of the solution.”
Armstrong will record an extended interview with Oprah Winfrey on Monday in which it is reported he will confess to doping during his career. The interview will be aired on Thursday.