With no declared rival for the post and none of the five permanent members of the Security Council opposing Ban, the 66-year-old former South Korean foreign minister is certain to get a new five-year term, envoys said.
His current mandate ends on December 31 but the Security Council powers -- Britain, China, France, Russia and the United States -- want to see the selection process handled quickly, diplomats said.
Ban will hold a press conference on Monday, following a meeting with the Asian group of nations at the UN, at which he is expected to announce his formal candidacy.
Approval by the 15-member Security Council and then a vote at the 192-country UN General Assembly should then be pushed through by the end of June, according to UN envoys.
"It is 100 percent certain that he will get the post again," said one envoy from a Security Council member.
Ban made a quiet start to his term as the successor to Kofi Annan in 2007. Some envoys say his awkward English has not helped his image. He championed the battle against global warming but the collapse of the 2009 Copenhagen climate summit was a blow.
He also insists that quiet diplomacy is sometimes necessary but has been criticized by rights groups for not speaking out more forcefully against rights abuses in major countries like China.
Ban suffered particular criticism from rights groups for not speaking publicly about China's detention of Nobel Peace Prize winner Liu Xiaobo last year.
But he has been praised by western nations for his strong stance on the Ivory Coast crisis and defending protesters taking part in the uprisings that erupted this year across the Middle East and North Africa.
He has repeatedly tangled by telephone in recent months with Moamer Qadhafi of Libya, Bashar al-Assad of Syria and Ali Abdullah Saleh of Yemen, chiding them as diplomatically as possible for not giving their people more freedom.
The action annoyed China and Russia which oppose what they consider unjustified interference in a country's domestic affairs.
"But he is skilled at acting and speaking in a way so that none of the permanent five (Security Council powers) can really complain," said a UN diplomat.
And Ban has been to the capitals of all of the permanent members, who could in theory veto his re-appointment, in recent months to shore up his support.
The UN leader has a strict work discipline, getting into the office at 7:30 am and often staying to make calls around the world until past 8:00 pm. He is also one of the best-travelled world leaders, clocking up hundreds of thousands of air miles each year.
On top of his defence of Arab protesters, Ban has also earned praise for his aggressive championing of women's rights. He set up a special UN super agency for women which is now run by former Chilean president Michelle Bachelet.
Copyright AFP (Agence France-Presse), 2011