Sadiq Khan has told councils to deny any planning requests to extract shale gas from deep under the capital.
The move appears to be a response to a request by London Local Energy to drill for gas in a former industrial area near the S tonebridge housing estate in Brent .
London Local Energy (LLE) applied for a licence to carry out fracking, which involves using chemicals and explosions to extract gas from deep below the ground.
Nick Grealy, chief executive of LLE, says the gas that would be released would be the lowest carbon neutral gas on earth, but Sadiq Khan argues that the process of fracking would be "harmful" for the capital.
Environmental news
Mr Grealy has earmarked the former White Heather Laundry site in Artesian Close, Stonebridge, saying: "In Brent, all we'd need is 1000sqm.
"Just one building. People would see nothing as it would all be contained within the building.
"Oil was discovered in NW10 in 1912 but nobody pursued it because the only way to extract it was through oil field valves.
"We would drill an ultra slim core hole which would then go down a mile or so, about three inches wide at the surface.
"It's completely unintrusive."
Brent Council has maintained it is "absolutely opposed to fracking in the borough", which can release toxic silica dust and contaminate water supplies.
Pollutants such as VOCs and hydrogen sulphide can also be released, which can cause neurological symptoms ranging from nausea to delirium and seizures.
There are also fears that the sheer volume of water used in the process may lead to water restrictions in areas prone to water restrictions.
The Mayor of London made the announcement ahead of the release of his Draft London Plan on Wednesday (November 29).
Mr Khan said: “There is absolutely no place for fracking in London and I remain firm in my belief that any such application must be refused.
“It is my duty to protect the health and wellbeing of Londoners, and it is well documented that the fracking process itself can cause chronic damage to public health, worsen toxic air quality and contaminate water supplies.
"Clearly, there can be no place for fracking in London.”
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