Cystic fibrosis sufferer Brian Shivers, 46, was handed a life sentence after a judge found him guilty of being part of the gang that gunned down Sappers Patrick Azimkar, 21 and Mark Quinsey, 23, outside Massereene Army barracks in Antrim on March 7 2009.
Just months before unemployed divorcee Shivers, from Magherafelt, Co Londonderry, took part in the killings, a doctor told him he had only three or four years to live.
His co-accused, high-profile republican Colin Duffy, from Lurgan, Co Armagh, was acquitted of the charges in the non-jury trial at Antrim Crown Court by Mr Justice Anthony Hart.
It was the third time in the last two decades that 44-year-old Duffy has walked free after being charged with murdering security-force members.
There were nasty scenes outside the court as the republican emerged, with loyalist demonstrators hurling vitriolic abuse at him and his supporters as he was hastily driven away in a waiting car.
Earlier, relatives of the two sappers wept openly in court as he was acquitted. But the room fell completely silent an hour later when Justice Hart delivered the guilty verdict for Shivers at the conclusion of what was a three-hour judgment.
After the verdicts, Sapper Quinsey's sister Jaime said they had got a measure of justice.
"Mark and Patrick were murdered as a result of a vicious cowardly act, they were unarmed and preparing to go to serve their country in Afghanistan."
"After nearly three years of heartache we have come a little bit closer to justice."
Sapper Azimkar's mother Geraldine added: "This was a terrible crime which stole Patrick and Mark's young lives from them."
She added: "Losing Patrick has devastated our family and has forever cast a dark shadow over our lives."
Police vowed that the investigation into the Massereene attack would go on.
"We will continue to pursue all of those involved in these evil murders," said Police Service of Northern Ireland Chief Superintendent Peter Farrar.
The English soldiers from the 38 Engineer Regiment were about to begin a tour of duty in Afghanistan when they were gunned down in an attack by republicans opposed to the Good Friday peace deal of 1998.
Sapper Quinsey, from Birmingham, and Sapper Azimkar, from London, were dressed in their desert fatigues and were within hours of leaving the base.
They were collecting pizzas at the front gate when they came under fire. Two other soldiers and two pizza delivery drivers, were injured in the gun attack.
Shivers and Duffy were charged with two counts of murder, six of attempted murder and a further count of possessing two machine guns.
DNA on matchsticks found in the partially burned-out Vauxhall Cavalier getaway car used in the ambush and abandoned eight miles away proved Shivers' undoing.
Justice Hart, who accused him of inventing an alibi for his movements on the night of the attack, said he was satisfied he had tried to set the car alight.
"Taking all of these matters together, I am satisfied that the prosecution has proved beyond reasonable doubt that Shivers set fire to the Cavalier at Ranaghan Road (where the car was abandoned) and I therefore find him guilty on each count," said the judge.
Before a silent courtroom, Shivers rose to his feet in the dock as Justice Hart, sitting in his last trial before retiring, passed sentence.
"There is only one penalty that I can impose upon you," he said.
"And that is one of life imprisonment, which I now do. I now sentence you to life imprisonment."
In a dramatic intervention, his lawyer Pat O'Connor QC attempted to stop the judge passing sentence but was swiftly told to sit down by Justice Hart.
Later, Mr O'Connor told the judge he had not meant any disrespect but had wished the sentence to be deferred until it was established what medical provisions were available for his client in jail.
The lawyer said Shivers, who had been out on bail on medical grounds since he was charged, had suffered a life-threatening deterioration of his condition when he was last incarcerated, upon his initial arrest.
"His life is at risk, there is no question, if he's not given a proper (medical) regime," he claimed.
Justice Hart said there would have been no possibility of Shivers being released on bail pending a check on medical provisions.
"These are very grave crimes indeed," said the judge. "And the court would have been failing in its duty if it had not remanded your client in custody."
He said the issue of medical arrangements was one for the Northern Ireland Prison Service to address and he would listen to further argument on the matter next month at a hearing ahead of setting a minimum term Shivers must serve.
Earlier, Duffy left the dock a free man after being cleared - even though the judge said DNA evidence found on the tip of a glove linked him to the getaway car.
The piece of latex was found in the footwell of the passenger seat of the Vauxhall while DNA traces from Duffy, who did not take the stand in defence, were also recovered from a seatbelt buckle.
Justice Hart said he was satisfied that Duffy had been in the car at some point after it was purchased two weeks prior to the attack up to the night in question and had worn latex gloves in the knowledge that it was going to be used in a criminal act.
But he said that did not prove he was part of the murder plot.
"There must be strong suspicion that Duffy did know what was going to happen and that that is why he has refused to give evidence," he said.
"However, suspicion, no matter how strong, is not sufficient by itself to establish guilt beyond reasonable doubt, and is not an acceptable substitute for facts from which guilt can be properly proved.
"I consider that there is insufficient evidence to satisfy me beyond reasonable doubt that whatever Duffy may have done when he wore the latex glove and handled or touched the seat belt buckle meant that he was preparing the car in some way for this murderous attack, and I therefore find him not guilty on each count."
There was an audible gasp from Duffy's friends and family when Justice Hart acquitted him, prompting the judge to ask for his supporters to be removed from court.
The bearded republican, who has been taken part in a "no wash" protest over prison conditions, showed little emotion as he got to his feet and calmly walked out of the dock.
Family members of the two sappers broke down on the other side of the court, with the Azimkar family leaving by another door and not returning for the rest of the judgment.
The trial lasted six weeks. It ended just before Christmas and Mr Justice Hart took four weeks to consider his verdicts.
PA
