He was also convicted of plotting to kill Ulster Defence Association leading figure Sam 'Skelly' McCrory, one of Adair's closest allies.
Duffy's cousin Martin Hughes and Paul Sands were also convicted over the same double murder plot.
Two other men - Craig Convery and Gordon Brown - were found guilty of being involved in organised crime.
The guilty verdicts were delivered at the High Court in Glasgow following a nine-week trial.
Anton Duffy, who is orignally from Mullaghduff, was described in court as the "driving force'' behind the double murder plan.
He initially planned the murder bid operations from his cell in Castle Huntly open prison in Scotland.
During a secret bugging operation, Duffy boasted to his girlfriend that he was going to get as many guns and explosives as he could.
It was also claimed during the trial the Duffy boasted that he was a member of the Real IRA.
The plot was uncovered during a covert MI5 undercover surveillance operation.
Duffy and Gorman were also accused of planning the murder of a former prison governor Derek McGill with a car bomb.
The four men denied all the charges.
They also denied a charge of joining others with the "intention of committing acts of terrorism".
Prosecutors said Duffy, and three others along with unnamed individuals, plotted to kill Adair and McCrory between August 2010 and October last year.
Locations where the plans were allegedly discussed included high-security HMP Shotts and a flat in Old Castle Road in Glasgow's Shawlands.
It is claimed "surveillance and reconnaissance" was carried out on Mr Adair and Mr McCrory.
The charges includes accusations there were plans "of where and by what means" each man "was to be murdered"
In 2010, Anton Duffy was jailed for five years for firearms offences. He had only been released recently.