Desmond John Villiers FitzGerald passed away in the early hours of yesterday at the age of 74.
He is survived by his wife Olda and daughters Catherine, Nesta and Honor.
Dating back to the early 14th century, the Knight of Glin is an ancient Irish noble title handed down from chieftain times and recognised by Irish governments.
Mr Fitzgerald became the 29th knight when he was 12 years old in 1949.
It is understood the title will die with him, as he has no male heir.
Arts Heritage Minister Jimmy Deenihan expressed his sympathy, saying: “I knew the Knight personally and I can remember so well having wonderful informed conversations with him in his home. He was always generous with his advice and kind in his remarks.
“With his passing, the Irish Georgian Society and Ireland has lost one of its titans and greatest champions of the arts and heritage.”
In 2009, the Knight was forced to close Glin Castle due to ill health and the economic downturn and forced to auction off some of his family’s treasures.
Speaking last year, he was highly critical of the lack of government support for heritage sites.
“I wish our politicians weren’t blindfolded and aesthetically ignorant, and would perk up and see that some of these places are very much part of our heritage. They are also a vital inheritance for the future and to bring people here,” he said.
Mr FitzGerald’s daughter Catherine is married to English actor Dominic West. The couple met at Trinity College Dublin and were married last year at the Church of the Immaculate Conception in Glin and 300 guests enjoyed a lavish reception on the grounds of Mr FitzGerald’s ancestral home, Glin Castle.
The Knight of Glin became president of the Irish Georgian Society in 1991.
Donough Cahill, executive director of the Irish Georgian Society, said Ireland had lost one of its most eminent academics.
“We in the Irish Georgian Society will sorely miss him and will find it hard to come to terms with his absence as he has been involved with the society since its early days and has been president for the last 20 years.
“Over this time, including the last two years of ill health, he has worked indefatigably for the society at home and abroad, particularly in the US,” he said.