A dying dissident IRA operative Brian Shivers was found guilty on Friday of murdering two British soldiers outside Massereene Barracks in Antrim in 2009.
Shivers suffers from incurable cystic fibrosis and will die in prison, the court was told.
His DNA was found on a cell phone left in a getaway car, which he and an accomplice had tried to burn but failed to complete the job.
Fellow dissident Colin Duffy, considered a senior figure in the IRA dissident ranks, was acquitted in the killing.
Both men were tried by a judge in a non-jury court in Antrim.
British Army soldiers Patrick Azimkar, from London, and Mark Quinsey, from Birmingham, were killed outside Massereene Barracks in Armagh on 7 March 2009, when they went to collect pizza at the entrance to the British Army barracks there. Two pizza workers were also injured in the gunfire.
Closed circuit footage showed the soldiers being gunned down and then repeatedly shot as they lay injured before the car drove away. Sixty bullets were fired in 30 seconds.
Duffy, 44, and Shivers, 46, both pleaded not guilty in the attack.
Shivers was described as an "unlikely terrorist" who was never arrested and lived with a woman of the Protestant faith and whose father was a senior figure in the early Civil Rights movement.
The judge said Shivers had lied about his involvement and the DNA on the phone proved it.
Judge Hart concluded: "I am satisfied that the prosecution has proved beyond a reasonable doubt that Shivers set fire to the Cavalier at Ranaghan Road and I therefore find him guilty on each count on the indictment."
Acquitting Colin Duffy, Judge Hart said "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.
"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.... “
Shivers was sentenced to life in prison.
There were loud cheers from supporters when Duffy was found innocent.
Despite DNA matches to him in the car, Judge Anthony Hart said the prosecution had failed to prove their case beyond a reasonable doubt.
The case marked the fifth time that Duffy has been charged with murder of security forces but every time he has walked. Several efforts to kill him by Loyalist groups have also failed.
Duffy gave an impromptu press conference protesting his innocence outside the court.