Former Portuguese Prime Minister Antonio Guterres has been officially appointed as the next UN secretary-general.
He will become the world's top diplomat on 1 January when Ban Ki-moon's second five-year term ends.
Mr. Guterres, 67, who led the UN refugee agency UNHCR for 10 years, was chosen from among 13 candidates last week.
He said his biggest challenge would be ending the civil war in Syria.
The world, he added, is facing a dangerous time and he wants to see people across the globe working together to achieve a safer future.
Mr. Guterres, who trained as an engineer, entered politics in 1976 in Portugal's first democratic election after the "Carnation Revolution" that ended five decades of dictatorship.
Outgoing secretary-general Ban Ki-moon told the assembly that his successor was well-known in diplomatic circles as a man of compassion.
"His political instincts are those of the United Nations - cooperation for the common good and shared responsibility for people and the planet," he said.
Source: BBC