Mr Guterres, who is also the former head of the UN’s refugee agency, comfortably won a straw poll held by members of the security council on Wednesday. None of the permanent members of the council said they would veto his candidacy.

A formal vote on the successor for Ban Ki-moon, whose term ends in December, will be taken at a UN Security Council meeting on Thursday when Mr Guterres is expected to be officially named as the new secretary-general.

Vitaly Churkin, the ambassador to the UN for Russia which had been considered the main potential obstacle to Mr Guterres winning the contest, said the Portuguese politician was now the “clear favourite”.

Western diplomats hope that Mr Guterres, who has a reputation as a skilful politician and has deep knowledge of the UN system, will provide more effective leadership of an international organisation that has seen its influence and relevance shrink in recent years.

The rapid development of a consensus around Mr Guterres ends a six month election process that aimed for greater transparency but which was ultimately defined by backroom dealmaking among the great powers.

Although he has been the frontrunner in a series of straw polls held by the security council over the past two months, Mr Guterres did not fit the initial profile that many of the key UN members had been looking for.

The US and the UK were keen for the next secretary-general to be a woman, while Russia backed eastern Europe’s claim that the new leader should be from the region.

The election also saw the last-minute entry of Kristalina Georgieva, vice-president of the European Union. The Bulgarian government nominated her last week after its initial candidate, Unesco chief Irina Bokova, failed to garner much support among security council members.

In the end, Mr Georgieva’s candidacy came too late to present much of a challenge to Mr Guterres. In the straw poll on Wednesday, the Portuguese politician received 13 positive votes and two of “no opinion”. Crucially, none of the veto-holding permanent members of the security council voted against him. By contrast, Ms Georgieva received only five positive votes and eight negative votes, including two from permanent members.

In a statement on Twitter, Ms Georgieva wished Mr Guterres “best of luck in pursuing an ambitious agenda for the UN”.

As support for Mr Guterres solidified in recent weeks, diplomats said that China and Russia had begun lobbying for positions in the second tier of UN management. The Chinese are believed to be interested in the head of the UN’s peacekeeping operations, a position currently occupied by a French official, while Russia is said to be pushing for one of the senior positions in the new secretariat.

Other candidates for the UN secretary-general included Helen Clark, the former New Zealand prime minister, Susana Malcorra, Argentina’s foreign minister and Slovakian foreign minister Miroslav Lajcak. Christiana Figueres from Costa Rica, who led the UN climate change negotiations last year, pulled out of the race last month.