Patrick Ryan helped secure munitions from Libya which were intercepted by the Irish navy off the coast of Ireland, according to BBC Northern Ireland's Spotlight programme.
Ryan travelled with former IRA commander Joe Cahill to Tripoli. A five tonne shipment of weapons on board the Claudia was to follow.
He said: "I would have liked to have been much more effective than I was but we did not do too badly."
The former East Africa missionary from the Republic of Ireland initially worked as a parish priest and contributed money to the republican cause while doing so.
He was approached by IRA leaders who asked him to work for them permanently. He was no longer a parish priest while associated with the Provisionals.
He told Spotlight: "They asked me to travel the world and try to get info."
In 1973 he was sent to Colonel Muammar Gaddafi's Tripoli along with IRA chief of staff Cahill.
Ryan spent the next 10 years visiting Libya and Europe, using a camper van to travel all over Europe raising money, the Spotlight programme said.
He deposited cash in a Swiss bank account for use by the IRA.
He said: "We were doing considerable business with the bank... exchanging unusual sums of money."
He also discovered timers which made it easier for IRA men to arm their bombs without being killed themselves, Spotlight said.
Those became a component in the republican organisation's bomb-making technology.
One was used to detonate the 1984 bomb at the Tory party conference in Brighton.
Fragments of the timer were recovered from the rubble.
The extent of Ryan's role was revealed by discussions between Prime Minister Margaret Thatcher and the Irish Taoiseach, Spotlight said.
The programme said documents revealed that Thatcher considered Ryan to be the main channel between the IRA and Libya for a decade.
She described him as a "very dangerous man" with an expert knowledge of bombing.
He said he regretted that he was not even more effective.
He told Spotlight: "One way or another I had a hand in most of them."
Spotlight on The Troubles: A Secret History airs on Tuesday September 24 on BBC One NI and BBC Four at 9pm.
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