Veteran Algerian diplomat the UN-Arab League envoy for Syria, has insisted throughout his career that there is no "hopeless situation", but he has not managed to find a magical solution to end Syria's civil war.
And the 79-year-old Brahimi, who took on the job last August after predecessor and former UN chief Kofi Annan threw in the towel, is now ready to give up too.
Annan resigned on August 2, frustrated by the division between supporters in the West and the Arab world of those fighting to oust Bashar al-Assad and traditional backers of the Syrian president, principally Russia and China.
"The decision has been taken, but we don't know when it will be formalised," one UN diplomat said of Brahimi on Saturday, speaking on condition of anonymity.
Earlier in the week, a senior aide to Brahimi told AFP he "thinks of it (resigning) every day" but would not decide until at least the middle of May.
"He thinks that every step he takes is countered with 10 steps backwards by the Arab states. And now it looks like the Americans will increase their military support (to the rebels), so he feels that he is useless in his role," the aide said.
If Brahimi quits, UN Secretary General Ban Ki-moon is unlikely to appoint a replacement quickly and could even take on the job himself, a UN diplomat said on Thursday.
Indeed, Brahimi could keep a role as an advisor to Ban on Syria or the Middle East, according to envoys.
"He will resign and will remain as a special adviser to the secretary general on the Middle East," said the UN diplomat.
"Ban will not rush to appoint a third person," added another Security Council diplomat. "You have had Annan, you have had Brahimi -- are you going to get someone who can do better than them?"
Nikolaos Van Dam, a former Dutch diplomat specialising in the Middle East, told AFP that "Brahimi had the additional advantage of being an Arab personality with enormous political experience".
"His mission was made a kind of 'mission impossible'... I do not know of any potential successor to Mr Brahimi who could as yet succeed in this extremely difficult job, certainly not as long as the UN and Arab League parties only theoretically support the Geneva principles, but do not do so in practice," Van Dam said.
The Geneva principles were adopted on June 30, 2012 by the Syria action group made up of the five permanent UN Security Council members, the Arab League, Turkey, the United Nations and the European Union.
They seek an immediate end to the bloodshed in Syria and urge establishment of a transitional governing body, but do not call for Assad to step down.
Brahimi, who played a key role as an Arab League emissary in the 1989 agreement that ended the civil war in Lebanon and has carried out various UN missions around the world, has tried everything to resolve the Syrian conflict.
It has been a rough ride for him.
Soon after his appointment, the opposition demanded he apologise for saying he did not know if the time had come to demand that Assad resign.
Then, during his third visit to Damascus last Christmas Eve, his talks with the Syrian president broke down when he asked Assad if he intended to run for the presidency in 2014.
Three days later Brahimi drove in the nail.
"Change should not be cosmetic; the Syrian people need and require real change, and everyone understands what that means," he said.
"We need to form a government with all powers... which assumes power during a period of transition. That transition period will end with elections," Brahimi added.
He has faced the wrath of the Syrian press which strongly criticised his efforts, even calling him a "false mediator".
"Lakhdar Brahimi is like an ageing tourist travelling for pleasure to capital cities across the world," said Syria's official newspaper Ath-Thawra in January.
"He has done nothing but try to make political settlements for Syria's crisis fail."
The pro-regime daily Al-Watan accused him of being a "pawn to implement the policies of some Western countries and regional states on Syria".
In October, his attempts to establish a ceasefire during a Muslim holiday failed and he has travelled to Moscow, Beijing and almost all of Europe's power centres in a bid to end the bloodshed, but without success.
His calls in January to stop arming the protagonists and conduct an inter-Syrian dialogue at the UN received no response.
Whoever eventually succeeds him will inherit one of the toughest diplomatic posts going, but some analysts think his successor could broker a breakthrough.
"I think there will be a third emissary who will come up with a solution as there is now a US-Russia tendency to find a compromise," said Bassam Abu Abdullah, director of the Damascus Centre for Strategic Studies, which is close to the regime.