The American athlete, who was stripped of his seven Tour de France titles over doping, was due to appear at a sports and technology conference in Dublin on Friday.
An on-stage interview at the widely publicised ticket-only event in the Irish capital’s RDS arena was to be followed by a 45-minute question and answer session open to the crowd.
However, organisers One Zero said Armstrong cancelled with less than 24 hours to go on the advice of his legal team, due to an upcoming court case brought against him on behalf of the US Postal Service.
Rob Hartnett, of One Zero, said: “We are extremely disappointed that Armstrong has withdrawn at the last minute from appearing at One Zero.”
“He has let us down, he has let his fans down and he has let down those that wanted to hear him openly discuss his past and the future of sport,” he said.
One Zero said Armstrong had been contracted to speak at the event since August.
In a statement on Thursday evening, they said they were “acutely aware” of the pending legal case and addressed the issue during negotiations “some months back”.
Armstrong did a broadcast interview with an Irish radio station earlier this month.
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