One in seven Londoners is paid wages which are below the poverty threshold, according to a study.
The Living Wage Unit, set up by the mayor in 2004, carried out the study and found the poverty threshold wage in London was £5.80 an hour.
But for a person to live "comfortably" in London they need to be earning £6.70 an hour - termed as a Living Wage.
Mayor Ken Livingstone said the figures were based on London's high cost of housing and were "disturbing".
"These findings show the importance not only of the fight against low pay but indicate why I have laid such stress on the achievement of an adequate supply of affordable housing in London," he said.
The new national minimum wage, set to be introduced in October, is £5.05 an hour.
Public service union Unison's general secretary Dave Prentis said: "It's a scandal that so many people are paid below the poverty threshold in the capital of the fourth richest nation and have to rely on state benefits to get by."
Chairwoman of London Citizens Living Wage Campaign, Deborah Littman, said the mayor's Living Wage would be a standard against which London employers can be "called to account".
Cleaners from Canary Wharf held a protest outside London's Old Vic on Thursday as part of a campaign to raise their hourly wage from £5.74-an-hour to £6.70-an-hour.