Mr Irons, 66, who spent six years and millions of euro restoring Kilcoe Castle outside Skibbereen in West Cork, said the Government should make the money spent on such heritage projects Vat exempt.
Tax breaks are currently available for these projects only if the property is opened to the public.
However, Mr Irons said that while Kilcoe Castle is his private home, it is still an asset to the State.
“People who go out on a limb and put much of their ill-earned gains into Irish heritage should be supported by the Government,” he said.
“I paid them 20% and it hurt, but I wanted my home to be a home, not open to the public.
“You tend to spend probably three times as much as the building is worth on the market. None of us is doing it to make money — we’re doing it for the love of building, and to bring them back.
“So when you have to pay 20% on top of that, it’s not helpful.”
Kilcoe Castle was built around 1450 by the MacCarthy clan on a two-acre island in Roaringwater Bay. It was one of the last castles in Carberry to fall to the English after the Battle of Kinsale in 1602. Over the centuries, it fell into disrepair until Mr Irons and wife, Sinead Cusack, bought it in 1998.
Mr Irons admitted it was a risky project for “someone with more money than sense”. However, after some initial controversy over its pink paint job, it is now regarded as one of the most painstaking restoration projects of its kind in Ireland.
Speaking at the Cork Person of the Year awards last Friday, Mr Irons paid tribute to Michael Flatley for his restoration of Castlehyde, in Fermoy, estimated to have cost the dancer some €30m.
“The Government has to realise that the historical and archaeological heritage of this country is immense and, if it is nurtured and looked after, it goes in the bank towards tourism,” said Mr Irons.
Mr Irons won the Oscar for Best Actor in 1991 for his role in Reversal of Fortune.
In a career spanning some 40 years, he starred in Brideshead Revisited, and in big-screen hits including The Mission, Dead Ringers, Die Hard: With a Vengence, The Man in the Iron Mask, and more recently, in the hit TV series, The Borgias.
He will play Alfred the butler in Batman v Superman, due for release in 2016.