Boris Johnson has said it is time "to knock on the head once and for all" claims he wants to be prime minister.
Mr Johnson said his "cup was running over" as London Mayor and dismissed talk of him wanting to succeed David Cameron as a "silly season" story.
He said the chance of this happening was "infinitesimally remote".
Referring to recently getting stuck above Olympic crowds, he told ITV's Daybreak "how could anybody elect a prat who gets stuck in a zip wire".
Mr Johnson's already high profile has been boosted by the success of London 2012.
Several Tory MPs and donors have talked up the possibility of him being a future party leader but Mr Johnson has said he is committed to seeing out his second term as mayor - which ends in 2016.
And asked on Daybreak whether he fancied becoming prime minister one day, Mr Johnson replied "no, of course not".
He added: "Because I have got four years of Mayor of London ahead of me. Perhaps this is the moment to knock this once and for all on the head.
"How can I issue a denial strong enough to stop this silly season story.
"I am mayor of London and my cup runs over and plus...we have got the Paralympics and they are going to be fantastic too."
Asked to categorically rule himself out as a future Conservative leader and prime minister "at any stage", he replied: "I think it is inconceivable that I am going to be prime minister. At the moment, I certainly don't want to be prime minister."
Mr Johnson was asked about a recent incident in which, attempting to promote Olympic big screens in east London, he was left momentarily suspended in the air on a 150ft zip wire.
In response, David Cameron said that for any other politician this would have proved a disaster but that it had turned out to be a triumph for Mr Johnson.
Mr Johnson said the experience had been "slightly scary" but that it had had a silver lining.
"After I got stuck on that thing, we did have a big increase in the number of visitors, so it was not totally fatuous, contrary to appearances."
But referring to talk about his political ambitions, he added: "There you have got it. How on earth could you elect that guy? How could anybody elect a prat who gets stuck in a zip wire?"
London would receive a "massive" long-term economic boost from the Olympics, he added, and that people seeing pictures of the city would want to invest.