Businessman David Ross has quit all of his roles in the organisation of 2012 London Olympics.
Olympics Minister Tessa Jowell said she and London mayor Boris Johnson had received an e-mail from Mr Ross earlier resigning his various positions.
It follows Mr Ross's resignation as a director of Carphone Warehouse in a scandal over the use of his shares.
Ms Jowell told the Commons culture and sport committee a replacement for Mr Ross would now be sought.
'With sadness'
Mr Ross was on the board of the organising committee for London 2012 (LOCOG) as well as bodies overseeing the legacy of the Games and the distribution of National Lottery funding for the event.
He was London Mayor Boris Johnson's appointment to the board of London 2012, charged with making sure that the games did not go over budget.
"I appreciate why David Ross feels he ought to stand down"
Mr Johnson said he had "reluctantly" accepted Mr Ross's resignation.
"I appreciate why David Ross feels he ought to stand down," he said in a statement.
"He will, nevertheless, be a loss having played an active and very useful role over the last seven months.
"I am particularly grateful to him for identifying serious issues with the 2012 Olympics that needed to be urgently addressed."
Ms Jowell told MPs that Mr Ross had taken the step "given the difficulties of his businesses".
She added: "I would like to place on record our gratitude to him and recognition of the very significant role he has played."
Mr Ross stepped down as director of Carphone Warehouse, which he co-founded, after it emerged that he had used millions of pounds worth of shares as collateral against personal loans without informing the company's other directors - a potential breach of City rules.
'Serious mistake'
Mr Ross said he had taken the decision to step down "with sadness" but he did not want outside issues to "distract" from the work of the Olympics organisers in the countdown to 2012.
"Given the present circumstances, and while they are not connected to the Olympics, I must now devote my full attention to my private business interests," he said.
Mr Ross is the latest in a series of senior mayoral aides to step down since Mr Johnson's election in May.
Labour said this record reflected poorly on Mr Johnson's judgement.
"Having now lost almost as many advisers as he's appointed, the serious questions about Boris's judgement show no sign of going away," said John Biggs, Labour member on the London Assembly.
"There's no doubt this was a serious mistake by Mr Ross. But the greater error was from the mayor, appointing him to such an important position within his administration."
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