However, in reality, he will serve less than two years under the terms of the Good Friday Agreement.
Last month, Belfast Recorder, Judge David McFarland convicted 54-year-old Kearney of the reservist's murder, telling him he was "either the gunman, the driver of the Ford Escort RS200 [getaway car] or was an occupant of the car being present to provide support for the killing".
Kearney, of Gorteade Road, Swatragh, Co Derry, had denied the murder of the 25-year-old reservist and possessing the Armalite AR15 assault rifle used to shoot him dead minutes after visiting his wife June, and new-born son, John Jr, at the Mid Ulster Hospital on 14 September, 1981.
However, years later, his DNA was found on a cigarette butt recovered from the murder scene, for which he had no answer.
This is the second time that Kearney was jailed for a terrorist gun attack.
In December 1984, Kearney was given 20 years, of which he served ten, for attempting murder of UDR soldiers.
Their Land Rover came under fire from the same AR15 rifle used to kill Constable Proctor, as it drove through Swatragh in the direction of Maghera in November 1982.
On Friday, Judge McFarland said he did "not take into account the release scheme under the Belfast [Good Friday] Agreement".
Quoting from two senior law lords, he added that the courts still had to determine the appropriate term, regardless of any remission or parole it may attract.
The Belfast Crown Court judge said the shooting of Constable Proctor, even with "the passage of 30 years has in no way diminished the brutality of this murder".
However, Kearney heard little of Judge McFarland's condemnation of him, having turned a deaf ear to proceedings.
When brought into the dock, Kearney dismissed a fresh offer of ear phones, telling the judge: "I don't want to hear anything ...you continue on."
Regardless, Judge McFarland told him that the policeman had been an easy target for Kearney and others who "were waiting for him" after visiting his wife June and new-born son Johnnie, at the Mid-Ulster Hospital.
"I do not know," the judge told Kearney, who was not listening, "if you were the gunman, were driving the 'getaway' car, or were there to provide support".
However, he added that in all of the circumstances, his shooting "has to be one of the most appalling murders committed during that period of our history known as 'the Troubles'. The passage of 30 years has in no way diminished the brutality of this murder."
That a man can be targeted when his is attending a hospital to visit his wife and newly born son, continues to appal all right-minded members of society ... He was murdered in a most brutal fashion and given no chance to defend himself or escape.
"He was targeted for no other reason than he was a serving police officer. Looking back over the 32 years since the murder, one is struck by the absolute futility," declared Judge McFarland.
The judge added that while the policeman's son "bears his father's name, no doubt with pride, but it is a constant reminder for him, and the rest of the family, of the cruel nature of his father's death."
Earlier, a prosecution lawyer said the murder had a devastating impact on the family, who had been looking forward to a full life, following the birth of a new son, but which was turned into total carnage and chaos by the shooting.
The lawyer said Constable Proctor, was shot by terrorists who deliberately targeted him, in a planned operation, because he was a serving officer carrying out a public service.
Kearney, he said, was one of those involved, and that there no mitigating features in the case.
Later, when asked if the defence had any submissions to make, Arthur Harvey QC replied that he had none to make.
More than three decades after her husband's murder, June McMullin told UTV it was worth the wait to see his killer convicted.
Recalling the shooting, June said: "It was like a nightmare, it was like something you didn't dream of, you just though 'God how can this be happening to me?'
"To sit in the court room and look at him, to think - you ruined a family, you took a life. How could you do that? For what?," she said on Thursday's edition fo UTV Live Tonight.
"It was like a weight had been lifted off my shoulders - finally we got justice."
She continued: "He's a murderer and no matter how long he does he will always be classified as a murderer. With us getting a guilty verdict it's very important for other families to know that there is hope out there and maybe someday they'll get the chance to get into court as well."