Secretary-General Ban Ki-moon, who proposed a 3.2 per cent budget cut in October, thanked the 193-member world body for agreeing to "cut fat" at a time when governments and people everywhere are struggling because of global financial difficulties.
He said he would instruct all managers to find new ways "to do more and better with less."
US deputy ambassador Joseph Torsella called the budget agreement "historic," saying it was the first time since 1998 and only the second time in the last 50 years that the UN regular budget declined from the previous budget's actual expenses.
The UN spent $ 5.41 billion in 2010-2011. The United States pays 22 per cent of the UN's administrative budget, and Torsella said the new budget "saves the American taxpayers millions of dollars and sets the United Nations on the path of real fiscal discipline and continued reform."
Over the last 20 years, he said, the UN's two-year budget increased by an average of 5 per cent which means the new budget represents savings to American taxpayers of as much as $ 100 million.
UN peacekeeping operations are funded separately. The regular operating budget was adopted Saturday after an all-night session.
General Assembly President Nassir Abdulaziz al-Nasser praised the "robust and constructive engagement" of all delegations in reaching consensus on a financial plan, saying the negotiating process had been "particularly challenging this year in the wake of global financial challenges."