Mr Ban has pledged to work as a “bridge-builder” UN Secretary General Ban Ki-moon has been re-elected to serve a second five-year term, in a vote at the UN General Assembly in New York.
Mr Ban, a former South Korean foreign minister, was the only candidate after the UN Security Council unanimously recommended his re-election.
Critics say he is too deferential to major powers, but he has won praise for his policies on climate change and the protests sweeping the Middle East.
He took over at the UN in 2007.
His second term will formally begin on 1 January 2012 and run until the end of 2016.
Mr Ban smiled and bowed to ambassadors and diplomats gathered at UN headquarters, who backed the reappointment through applause without a vote.
“In a complex, difficult international environment, you have strengthened the role and the visibility of the United Nations by adopting reform measures, launching exciting, innovative initiatives, and calling faithfully and constantly for respect for human rights, the rule of law and the other values rooted in our charter,” UN General Assembly President Joseph Deiss told him.
When he announced his candidacy two weeks ago, Mr Ban pledged to keep leading the world body as a “bridge-builder” in a time of unprecedented global change.
Correspondents say when Mr Ban was first elected, powerful nations in the Security Council seemed to want a low-profile leader after the schisms of the 2003 Iraq war.
However, his low-key approach has sometimes been criticised. He came under heavy attack from human rights activists for failing to take a public stand on the jailing of Chinese Nobel Peace Prize winner Liu Xiaobo.
More recently, he has spoken out in support of pro-democracy activists in the Middle East and North Africa.
He has also taken a strong stand on climate change.
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