Douglas Slade, 75, an early member of the Paedophile Information Exchange, abused five boys between 1965 and 1980.
Slade was arrested in the Philippines in 2015 and deported to the UK accused of 13 counts of child abuse and rape.
He had denied all charges, over which the judge said he was "wholly unrepentant", but a jury convicted him at Bristol Crown Court.
The man who ran a paedophile hotline from home
Judge Euan Ambrose also told Slade: "Your past has caught up with you."
He added the abuse had had a "profound effect" on Slade's victims, "throughout their adult lives".
As the defendant was being taken to the cells a man claiming to be one of his victims in the 1970s, stood up in the public gallery, shouted his name and held up a sign before being ushered out.
The sign said: "The Filipino children you abused for years have no voice. I have no voice for the harm you did to me. Rot in jail Slade".
Another abuser, Christopher Skeaping, 72, formerly of Hounslow, London, was found guilty of one charge of indecent assault dating back to 1980. He will be sentenced at a later date.
Slade's history of paedophilia was exposed in the Sunday People, when an article in 1975 named him as one of the "vilest men in Britain".
Avon and Somerset Police said Slade, formerly of Sea Mills and Totterdown in Bristol, "was one of the main instigators" of the notorious exchange.
The group campaigned to legalise sex with children, and Slade ran a helpline for paedophiles from his parents' home.
A police spokesman said the force is investigating other lines of enquiry in relation to Slade's activities, and believes there are likely to be further victims.
A paedophile once dubbed one of the "vilest men in Britain" has been jailed for 24 years for child abuse offences.