"Thanks! Thanks! Thanks!" he tweeted, saying he was "honoured and happy."
Matthew Rycroft, Britain's ambassador to the UN, said he was "delighted" at the result, and described Guterres as "exactly the strong Secretary-General the UN needs."
And yet the Portuguese politician was at the helm of the UN's refugee organisation precisely when the refugee crisis began to spiral out of control.
The UN has so far been unable to galvanise support for any significant solutions to the problem, described as the worst humanitarian crisis since World War II. The UNHCR - which Guterres ran until December - estimates that 34,000 people are forced from their homes every day, and there are now 21.3 million refugees, half of them children.
Guterres has said that he intends to make preventing crises a priority for the 71-year-old organisation - which has been hampered by a decade of lethargic responses to crises under Ban.
"We need a surge in diplomacy for peace," he said, outlining his plan. "The international community spends much more time and resources managing crises than preventing them.
"A Secretary-General must continuously seek to contribute to reducing the number of conflicts and consequently the number of victims."
ABOUT ANTONIO GUTERRES
Age:67
Born: Lisbon, Portugal,
Political party: Socialist
Becomes UN Secretary General: January 1, 2017
Career timeline:
UN High Commissioner for Refugees
(2005-2015)
Secretary of Socialist International
(1999-2005)
Prime Minister of Portugal
(1995-2002)
"We need a surge in diplomacy for peace. The international community spends much more time and resources managing crises than preventing them."
Guterres secured the nomination by finally winning over the Russians, who were believed to be blocking his candidacy.
They had pushed for Irina Bokova, head of UNESCO, to take the job - but her perceived proximity to Moscow made her candidacy difficult for Britain and the US to accept.
The selection process for the new Secretary-General was more open than ever before in the 70-year history of the UN.
The 13 candidates had to submit detailed proposals for their work, and appear before the General Assembly to outline their plans.
Britain and the United States were particularly vociferous in calling for a woman to take the job for the first time in UN history.
Half of the 10 candidates who remained until today's decision were women, but none of them were able to garner the support of all the members of the Security Council.
Kristalina Georgieva, a 63-year-old Bulgarian who heads the EU budget and human resources division, threw her hat into the ring last week - and was considered by some to be a strong contender.
But it now appears that her candidacy was announced too late, and she did not have enough time to build a base of support.
Marcelo Rebelo de Sousa, Portugal's President, complained about her late entry to the race - and compared her to "an athlete who joins the marathon in the last 100m".
Ban, who was in Brussels for an Afghanistan conference, has been praised for his role in securing agreement on climate change.
But he has been criticised for the UN's inability to improve the Syrian situation, and portrayed as lacking the clout of some of his predecessors - notably Kofi Annan and Dag Hammarskjold, the second Secretary-General, who died in a plane crash in 1961.
Ban is believed to be contemplating running for prime minister of South Korea when he steps down on December 31.
