Bryan Hudson, 62, was convicted by a York Crown Court jury of five charges of non-recent child sex abuse dating back to 1996.
The charges include four of indecent assault against a girl and one of gross indecency with a child.
Hudson, off Carr Lane, York, abused two victims, aged two and five at the time while attending a party.
Although a police investigation took place at the time of the offences, there was not enough evidence to proceed with a charge against him.
However, in 2015 Hudson was convicted of the possession of indecent images of children.
During that investigation, former North Yorkshire Police Detective Constable Gary Blackburn became aware of Hudson’s previous arrests and with the support of the victims, their families and the force, carried out a cold case review.
The new investigation uncovered another victim, who had been abused by Hudson at the age of four. With more evidence of Hudson’s offending, charges were able to be brought against him.
Speaking after the sentence handed to Hudson, Detective Constable Gary Blackburn, now of British Transport Police, said: “Hudson targeted these young girls and subjected them to horrific assaults for his own sexual gratification.
“By pleading not guilty, and forcing them to give evidence against him, he again put them through another distressing experience. I’m incredibly grateful to the victims for the bravery they have shown throughout this case.
“No sentence can ever take away the pain and distress they have felt over the last 20 years. All of the victims involved have spoken about how they lost their childhoods due to Hudson’s evil actions. I hope this result can help them all move forward, knowing that the man responsible is behind bars.
“Anyone who has suffered sexual abuse, no matter how long ago it happened should feel confident to come forward and report it. We will listen and we will investigate.”
Hudson's name will be on the sex offenders register for life.