The longest-held British captive, who arrived in Beirut on Tuesday for a two-week working visit, met Sayyid Muhammad Husayn Fadl Allah, said Giles Trendle, a producer working for British network ITV.
Fadl Allah is the most prominent spiritual guide of Lebanon's Shia community. During Lebanon's 1975-1990 civil war, political factions rose from among the Shia community, some of whom were blamed for a wave of anti-Western kidnappings.
McCarthy was on assignment in Beirut for Worldwide Television News (WTN) when he was taken hostage on 17 April 1986. He was finally released by his captors on 8 August 1991.
"John was quite relaxed, and the meeting went very well. It was very friendly," said Trendle.
"But there was no mention of his captivity, as this is not part of the documentary. We are not looking back," he said.
Trendle said the one-hour documentary was about the Shia community in Lebanon, Iraq and Iran, "especially after the events in Iraq. It is meant to explain who they are to the Western world.
"We learned a lot from Sayyid Fadal Allah about the Shia," he said.