Joe Akerman was one of three who had been in prison along with Joshua Molloy, from Ballylynan, Co Laois, a former Royal Irish Regiment soldier, and fellow Briton Jac Holmes.
It is understood they were freed last night, with Ireland’s Foreign Affairs Minister Charlie Flanagan first to break the news to the Molloy family.
A British Foreign and Commonwealth Office spokeswoman also confirmed the release of the two Britons.
“We are helping two British men make arrangements to leave Kurdistan after they were released from custody,” she said.
According to reports on the BBC, Mr Akerman updated his status on Facebook, posting one word: “Free”.
It is understood they had been with the Kurdish People’s Protection Units (YPG), a force reported to have in the region of 25,000-50,000 fighters trying to quell IS in northern Syria.
Declan Molloy, Joshua’s father, said emotions in the family were running wild.
“We are all delighted here. We are jumping with joy to know that he is out,” he said.
“You know that Christmas morning feeling, it’s a bit like that, when you find your most sought-after present under the tree, the dream present. That’s how we feel.”
Mr Holmes, an IT worker in his early 20s originally from Dorset, had no military experience before he went to Syria.
He was shot in one arm in a gun battle with IS forces last May.
His mother Angie said she was elated at the news and described her son and his front-line comrades as “heroes”.
“Jack’s family and friends are grateful for all the help and support they’ve received during this difficult time,” she said.
“(We) would like to thank everyone including the Foreign and Commonwealth Office and the Kurdish Regional Government for their assistance in securing his release.”
Mark Campbell, a Kurdish rights campaigner for 20 years, tried to raise awareness of the men’s plight by visiting the KRG High Representatives’ offices in London last Friday with Mrs Holmes.
“I am so happy that common sense has prevailed and these brave men have been freed and able to return to their families,” Mr Campbell said.
“They deserve medals not prison and I hope they will get apologies and the recognition they deserve.”
Mr Campbell had tried to dissuade Mr Holmes from travelling to Syria before he went out but had no contact with Mr Molloy or Mr Akerman before they left.
Mr Akerman, 34, is a former British soldier from Halifax.
The men were detained after leaving the front line to come home.
It is believed they had been in the Rojava region of Syria for some time and at least one had fought in the liberation of Sinjar, the city where thousands of Yazidis were slaughtered and fled from after IS took it over in 2014.
They were imprisoned in Erbil for about 10 days by authorities from the Kurdish Regional Government and it is understood demands had been made for 15,000 dollars (£10,400) in fines to be paid to secure their release.
Mr Molloy’s father, a passionate amateur astronomer, considered selling his set of telescopes in order to raise money to try to free his son.
“It was a tough battle but I have got to give my thanks to Mark Campbell in the Kurdish support group in London,” he said.
Mr Molloy got a second-hand account of his son’s condition and life in the jail after a freelance reporter managed to visit him in the hours before the releases were secured.
“It must have been an awful place to be,” he said.
Mr Molloy also paid tribute to the work of diplomatic chiefs in London and Dublin.
British consular staff in Iraq spent most of last week trying to secure their freedom.
After phoning the Molloy family late on Saturday night Mr Flanagan said: “I welcome Joshua’s release and I am pleased that he is now on his way home to join his family in Ireland.
“Would like to thank all those who helped to make this early release happen. My department will continue to provide consular assistance in this case.”
It is understood Mr Molloy is in a hotel making travel arrangements out of Kurdistan and is considering spending time in Europe with fellow foreign fighters before he returns to Ireland.
His father has always insisted that his son is not a mercenary or a freedom fighter, but that he had travelled to Syria last year for humanitarian reasons.
Mr Molloy spoke to his son via Facebook after his release and reported that he was “fine” but felt that he would need some time alone after his ordeal.
British diplomats had been working on the ground on behalf of all three men, saying that they do consular work for Irish citizens in difficulty in some countries where Ireland does not have representation.
It is understood the policy in diplomatic and consular assistance cases of refusal to pay “fines” or ransoms was maintained throughout the negotiations.