Ban Ki-Moon, 62, is the first Asian head of the UN since Burma's U Thant held the post from 1961 to 1971. Asian nations had insisted it was their turn for the job to succeed Kofi Annan, a Ghanaian, who has led the 192-member world body for the past decade.
He will be the eighth secretary-general of the United Nations since 1946.
The 15-member UN Security Council recommended Ban as the next secretary-general to the General Assembly after he comfortably beat six rivals in informal council polls. The General Assembly acclaimed him secretary-general by acclamation for a five-year term.
In remarks to the General Assembly after it approved Ban, Annan described his successor as "a future secretary-general who is exceptionally attuned to the sensitivities of countries and constituencies in every continent."
"A man with a truly global mind at the helm of the world's only universal organisation," he said, adding that he wished Ban strength and courage as he readied to take over the job and to "have fun along the way."
Born to a farming family in 1944 - toward the end of the Japanese occupation of the Korean Peninsula - Ban has moved inexorably up the ranks of the foreign ministry, which he joined in 1970 straight after university where he graduated top of his class in international relations.
He was appointed foreign minister in January 2004.