Gordon Anglesea, 79, from Old Colwyn, was convicted of one charge of indecent assault against one boy, and three indecent assaults against another.
Addressing Anglesea at Mold Crown Court Judge Geraint Walters said "there can only be one sentence and that is a prison sentence".
North Wales Police's assistant chief constable apologised after the trial.
"The victims in this case have waited a long time for justice and I am pleased that today they have seen this done," said ACC Richard Debicki.
"It has not been an easy journey from them, it has taken courage to stand  by their convictions, but I hope that they will now take some solace from  seeing their abuser brought to justice."
"I  would like to apologise on behalf of the force to those whose lives he so  traumatically affected."
Anglesea, a former superintendent in the Wrexham area, had denied the charges, with his defence funded by the Police Federation.
He was also found not guilty of an alternative charge of a serious sexual assault, and granted bail until 4 November when he will be sentenced.
Ed Beltrami, chief prosecutor for the Crown Prosecution Service Wales, said Anglesea had been in "a position of power and authority in order to prey on very young and vulnerable victims" and praised those who gave evidence for helping to secure his conviction.
"I hope that it will also prove to be a meaningful step in the recovery process of his victims, who have had to live with what happened for a long time before seeing their abuser brought before the court," he added.
Anglesea was arrested in 2013 as part of the National Crime Agency's Operation Pallial investigation into historical abuse across north Wales.
The offences took place between 1982 and 1987, when both boys were aged 14 or 15.
One boy was abused in the showers of a Home Office attendance centre in Wrexham run by Anglesea, who was a police inspector at the time.
The court heard how he subjected juvenile offenders to a military-style, "short, sharp shock" regime of physical exercise, drill parades and woodwork classes on Saturday afternoons.
Anglesea was "answerable to no-one" at the centre and would "inspect" the parade, make the youngsters do naked sit-ups and squat thrusts, then loiter around the showers "with a smirk on his face".
His second victim was initially sexually assaulted by convicted paedophile John Allen, while living at the Bryn Alyn children's home in Wrexham and the abuse sometimes involved other adults who used him "like a toy".
On one occasion, at a house in Mold, he said Anglesea "grabbed him by the hair" and indecently assaulted him, calling him "scum" and telling him he had the "power to send him away".
The prosecution said both victims had been left "damaged" by the abuse and led "chaotic" lives of crime and drug and alcohol addiction.
During the trial, Anglesea was questioned about links to other paedophiles, including Gary Cooke, who is currently serving 14 years in prison, and Peter Howarth, former deputy head of the Bryn Estyn children's home, who died in prison in 1997.
In 1994, Anglesea was awarded Â£375,000 in libel damages after media organisations ran stories about his links to abuse at children's homes in north Wales.
One report, published in 1991, detailed how Bryn Estyn residents claimed he was a regular visitor to the home.
Anglesea has always maintained the allegations at the heart of the libel case were false but said in court that even after the libel trial, the issue "never went away".
One of those publications sued by Anglesea was the satirical magazine Private Eye.
In a statement, its high-profile editor Ian Hislop, described that action as "one of the darkest periods of my editorship".
"During the libel trial Anglesea said that he had never assaulted any teenage boys. We now know that this was a lie, that he was indeed a paedophile, that in truth he had no reputation to defend.
"I take a certain grim satisfaction in this verdict today and in the fact that justice has eventually been done."
But Mr Hislop said he did not intend to revisit the libel case.
"Private Eye will not be looking to get our money back from the libel damages. Others have paid a far higher price," he said.
A former north Wales police chief has been found guilty of historical child sex offences.