Armstrong, 41, admitted in an interview with Oprah Winfrey this week that he used performance-enhancing drugs to win the Tour de France seven times.
Last year he was stripped of his titles after being labelled a "serial cheat" by the United States Anti-Doping Agency.
Johnson, one of sport's most notorious dopers having won the 1988 Olympic 100 title before his medal was taken away three days later for taking steroids, said Armstrong could still rebuild his standing with the public.
"American people will forgive him," Johnson told BBC radio. "I don't think it will be tough for him to make a living. I hope he can move on and do good things. If he can find some way to make a living he will be fine.
"I think people will judge him differently, based on what he did for humanity and for cancer."
- Sports & Recreation