UK runner Rob Sloan, initially claimed that training made him a "better runner" but was forced to confess that he completed Sunday's Kielder Marathon in Northumberland aboard the free spectator's bus.
The 31 year old flagged down a bus and was driven the last 9.6km to the race's closing stages.
Then he jumped off, hid behind a tree until other competitors came into view and rejoined the race, crossing the finishing line in two hours, 51 minutes and one second to secure third place.
According to reports, Sloan initially dismissed the allegations and insisted he had completed the race.
"I ran the whole race," he told the BBC, "I'm upset and angry that someone wants to cast these aspersions".
However he was spotted by a number of witnesses on the bus and the organisers decided to disqualify him after the event.
A statement from the organisers of the marathon said, "Last night we confirmed that the athlete who was disqualified on Sunday, after initially placing third, has admitted that he failed to complete the whole course. Rob Sloan of Sunderland Harriers had apparently made the decision to withdraw from the race at approximately 20 miles due to fatigue and after returning to the Leaplish Park area he decided to run the closing section of the course and crossed the finish line in third place".
Kevin Carr, the chairman of Sunderland Harriers, said, ‘It’s blatant cheating as far as I’m concerned and as a club we’re going to come down really hard on him.’
Sloan later apologised for the "confusion" he caused.