While the amount of money Sevan allegedly took was not immediately known - and may be as little as $160,000 - the findings will be a major blow because of his stature in the organisation and the control he had over it.
The programme was one of the largest in history. The Independent Inquiry Committee had planned to release its findings about Sevan next Tuesday, and had sent advance notice to Sevan's lawyer, Eric Lewis, last week.
Lewis revealed the findings on Thursday and vehemently denied both claims against Sevan, whom the UN is paying a symbolic $1 a year to keep him on payroll so he will cooperate.
"The fact is, the committee's allegations are baseless," Lewis said in a statement.
"Mr Sevan never took a penny, as he has said from the beginning."
"The fact is, the committee's allegations are baseless"
Eric Lewis, Benon Sevan's lawyer
The committee, led by former US Federal Reserve chairman Paul Volcker, refused to comment on Lewis' claims.
Committee spokesman Mike Holtzman had said earlier Sevan would be one of several people considered in the Tuesday report.
"Mr Sevan is obviously welcome to express his feeling in the media," Holtzman said. "Our final judgment on him will be rendered on Tuesday."
The oil-for-food programme, launched in December 1996 to help ordinary Iraqis cope with UN sanctions imposed after Saddam Hussein's 1990 invasion of Kuwait, quickly became a lifeline for 90% of the country's population of 26 million.
Under the programme, Saddam's government could sell oil, provided the proceeds went to buy humanitarian goods or pay war reparations.
Saddam's government decided on the goods it wanted, who should provide them and who could buy Iraqi oil.
But the Security Council committee overseeing sanctions monitored the contracts.
In a bid to curry favour and end sanctions, Saddam allegedly gave former government officials, activists, journalists and UN officials vouchers for Iraqi oil that could then be resold at a profit.
It is almost certain that Sevan would be fired if the United Nations accepts the Volcker committee claims.
Sevan, a Cypriot, ran the programme from 1996 until it ended in November 2003 and retired from the UN last year but remains on the payroll because of the $1 a year salary.
Volcker's team has been investigating oil-for-food for more than a year and will release its final report in late August or early September.