He declared his candidacy two weeks ago and was backed by the UN Security Council last week to continue in the role he took over from Kofi Annan in 2007.
The former South Korean Foreign Minister pledged to keep leading the world body as a "bridge-builder" in a time of unprecedented global change.
Born-13 June 1944 (age 67)
Eumseong County, Chungcheongbuk-do, South Korea
Nationality-South Korean
Spouse(s)-Yoo Soon-taek
Alma mater-Seoul National University (B.A.)
Harvard University (M.P.A.)
Religion-No public affiliation
US Ambassador to the UN Susan Rice welcomed Ban's re-election to the post of secretary-general and praised his performance in "one of the toughest jobs in the world."
"No one understands the burdens of this role better than he," she said, adding that Washington was "grateful that he is willing to take them on."
All the regional groups of UN member states backed Ban, including the Latin American and Caribbean group, the last to officially endorse his re-election.
UN officials and diplomats had said Cuba, Barbados and others held up the group's endorsement amid complaints that Ban had neglected the region. Havana denied causing a delay.
Joseph Deiss, president of the General Assembly, praised Ban for "his remarkable leadership" and for having "strengthened the role and visibility of the UN.
"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,” Mr Deiss told the Assembly.
Mr Ban, 67, has previously said climate change is the "most important priority" for mankind.
He has also said he supports Arab protesters during this year's wave of revolutions, vowing to speak up for the disenfranchised.
When he declared his candidacy he said that during his term the UN "responded quickly and effectively to a series of devastating humanitarian emergencies" in Myanmar, Haiti, Pakistan and elsewhere.
He added that his team also worked to keep attention on the world's poorest people during the global economic crisis.
But critics- including some human rights group - say he has put too much faith in quiet diplomacy and has been too soft on China.
Biography
Ban Ki-moon was born in Eumseong in a small farming village in North Chungcheong, in 1944 at the end of the Japanese rule of Korea. His family moved to the nearby town of Chungju, where he was raised. During Ban's childhood, his father had a warehouse business, but the warehouse went bankrupt and the family lost its middle-class standard of living. When Ban was six, his family fled to a remote mountainside for the duration of the Korean War. After the war ended, his family returned to Chungju. Ban has mentioned meeting U.S. military troops at this time.In secondary school (Chungju High School), Ban became a star pupil, particularly in his studies of English. In 1952, he was selected by his class to address a message to then UN Secretary-General Dag Hammarskjöld, but it is unknown if the message was ever sent. In 1962, Ban won an essay contest sponsored by the Red Cross and earned a trip to the United States where he lived in San Francisco with a host family for several months. As part of the trip, Ban met U.S. President John F. Kennedy. When a journalist at the meeting asked Ban what he wanted to be when he grew up, he said, "I want to become a diplomat."
Ban received a B.A. in International Relations from Seoul National University in 1970, and earned a Master of Public Administration from the John F. Kennedy School of Government at Harvard University in 1985. At Harvard, he studied under Joseph Nye who remarked that Ban had "a rare combination of analytic clarity, humility and perseverance." Ban was awarded the degree of Doctor of Laws (Honoris Causa) by the University of Malta on 22 April 2009. He further received an honorary degree of Doctor of Laws from the University of Washington in October 2009.
In addition to his native Korean, Ban speaks English, French, and Japanese. There have been questions, however, regarding the extent of his knowledge of French, one of the two working languages of the United Nations Secretariat.