The Security Council's choice for the new head of the global body became clear last week when Guterres survived a series of straw polls with no permanent member voting against him.

The former head of the UN refugee agency from Portugal has been the front-runner to take the helm after Ban Ki-moon's second five-year tenure ends at the end of the year.

In an address to the General Assembly, Ban praised member states "not only for their choice, but for the way in which they went about it".

"The first-ever public hearings on the selection of a Secretary-General opened the process to the world," he said.

Regarding his successor, he said: "Secretary-General-designate Guterres is well known to all of us in the hall. But he is perhaps best known where it counts most: on the frontlines of armed conflict and humanitarian suffering.

"For the past decade, the work of the United Nations High Commissioner for Refugees and other humanitarian actors has been a lifeline for millions upon millions of people forced from their homes."

The 67-year-old former Portuguese prime minister will succeed the South Korean diplomat Jan. 1, being elected to the UN's top post after running a public campaign beginning in July, which marks a break from a traditionally secretive election process.

Guterres appears uniquely poised for the top job on account of his decade-long experience with the refugee agency, UNHCR, in a global climate gripped by a refugee crisis the likes of which have not been seen since World War II.