Prosecutors said Colin Gregg, 75, hid his offending beneath a “veneer” of respectability and had exploited his position in society.
Gregg had helped to build up the family business in the 1960s but later became a teacher, headteacher, social worker and charity boss.
The grandfather was yesterday found guilty of nine counts of indecent assault by a jury at Leeds Crown Court.
The jury had heard how Gregg, of Homefarm Steading, Gosforth, Newcastle, assaulted the boys, who were aged between 11 and 14 at the time, over three decades.
The court was told the offences took place during a period starting in the 1960s and into the 1990s.
The jury was told how the pensioner was once headteacher at The King’s School Junior School, in Tynemouth, and also taught at Durham School.
Gregg also had spell working as a social worker in Newcastle.
He had denied all the charges, claiming he was the victim of a “witch hunt” and that the complainants were looking for compensation money.
The month-long trial in Leeds was a retrial after a jury in Newcastle last year failed to reach verdicts.
The Leeds jury found Gregg guilty by a majority on eight of the counts and unanimously on the ninth.
He showed no emotion as the verdicts were read out and he left the courtroom saying nothing after he was granted bail.
Judge Robin Mairs told Gregg that the fact he was granting bail was no indication of the sentence he will receive.
He said: “These are serious matters and a custodial sentence is inevitable.”
As Gregg left the court building under an umbrella, he was asked if he would apologise to his victims, but said nothing before he was driven away.
He is due to be sentenced at Newcastle Crown Court on March 30.
The jury was told Gregg was cleared of sexually assaulting a young man in 1997.
John Dilworth, from the Crown Prosecution Service, said: “Throughout his life, Colin Gregg has been a successful businessman, respected teacher and committed charity worker.
“Those achievements have won him the gratitude of the community but, beneath his respectable veneer, Colin Gregg was sexually abusing young boys with alarming regularity.
“Colin Gregg exploited his position in society to abuse young boys, using them for his own sexual gratification.
“Working closely with investigating police, we have been able to demonstrate not only a distinct pattern to Colin Gregg’s offending, but also a propensity on his part to commit such acts.
“I would like to praise the bravery of the victims in this case. It is thanks largely to their evidence that the court has today found Colin Gregg guilty of nine charges of non-recent sexual assault, charges for which he had evaded justice for a considerable number of years.”