Guterres, who was prime minister of Portugal from 1995 to 2002 and served as UN High Commissioner for Refugees from 2005-15, will take over when incumbent Ban Ki-moon steps down.
The UN Security Council nominated Guterres for the five year term earlier this month, which has now been endorsed by acclamation by all 193 member countries.
For the first time, selection of the secretary-general moved from being ‘behind closed doors’ into public discussions with each candidate campaigning for the post.
Guterres said that alleviating the suffering of the vulnerable people – in particular refugees and those in conflict zones – and gender equality would be key priorities for him.
He said diversity should be viewed as a “tremendous asset” and not a threat.
Ban, who became secretary-general in 2006, said Guterres was “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”.
International Monetary Fund managing director Christine Lagarde congratulated Guterres, saying: “His proven leadership, both within and outside the United Nations system, and extensive experience in international relations will be vital for the United Nations in rising to meet the many challenges it faces and in supporting member states achieve the 2030 sustainable development goals.”