Robert Black has been found guilty at Armagh Crown Court of kidnapping and murdering schoolgirl Jennifer Cardy in August 1981.
Black, 64, and originally from Scotland, had denied abducting and murdering the nine-year-old.
She disappeared after leaving her home in Ballinderry to cycle the short distance to a friend's house.
Her body was found six days later floating in a dam near Hillsborough, Co Down.
The jury of nine women and three men began deliberations at Armagh Crown Court yesterday morning.
They took four hours and 15 minutes over two days to reach their verdict. Black showed no emotion when the verdicts were read out.
Jennifer's mother Patricia sobbed quietly in the public gallery and was comforted by her husband Andy.
Judge Mr Justice Ronald Weatherup told Black: "You have been convicted by a jury of murder. There is only one sentence that will be imposed by law.
"That's the sentence of life imprisonment. Accordingly, I sentence you to life imprisonment."
He then turned to the guards and said: "Take him down please."
Black was convicted in 1994 of three unsolved child murders in the 1980s in England and Scotland.
The Cardy family spoke outside the court after the verdict and sentencing.
"We prayed for Robert Black, that Robert Black would some day know Jesus as his saviour, just as Jennifer knew Jesus as her saviour, and the wonderful thing is that some day we will be reunited with Jennifer in glory and that is just a wonderful thing to know that," Mr Cardy said.
He does not hate Black, he said, he just pitied him.
"We pity Robert Black and the awful life he has led.
"We have been able to live without bitterness and vengeance in our lives and when we lost Jennifer life was never the same but life had to go on and we had to live life.
"Robert Black stole the life of our daughter, Jennifer, but Robert Black didn't steal the lives of me and my family - we've lived a happy, prosperous life, but we miss Jennifer each and every day."
