Fianna Fáil's Cathal Crowe had previously called on the government to work with the Vatican to have the crown returned to Ireland, despite doubts from historians about its existence.
The crown, which belonged to Ireland’s most well-known High King, was said to have been given to the Vatican by his son Donnchad, as a gift to the Pope.
In a response to a further parliamentary question from Mr Crowe, Tánaiste Simon Harris confirmed that officials from Ireland’s embassy to the Holy See had carried out work on the matter.
Mr Harris said that officials engaged with the Chair of the Irish Manuscripts Commission and UCD Professor of History, John McCafferty, while also citing an article by UCC academic Jesse Harrington on the crown.
“His report provides no evidence for the existence of such a crown,” the Tánaiste said.
“By way of historical context it should be noted that the existence of the crown of Brian Boru, former High King of Ireland, is doubted by historians.
“It is understood that there are no records of Irish kings of the Middle Ages wearing crowns. They neither feature in inauguration rituals nor were worn as symbols of authority.
“Furthermore, the first written reference to a putative crown of Brian Boru dates only from the 1627 Annals of Clonmacnoise. No crown has been recorded or catalogued in the Vatican museums or archives.
“In the absence of new historical research, the matter rests.”
Medieval Irish history professor at Trinity College Dublin, Seán Duffy, also cast doubt on the existence of such a crown, saying instead that it could be a metaphor for the Vatican having permission to decide Ireland’s ruler.
“There was a belief in the Middle Ages that all islands belonged to the papacy. The pope could therefore give an island away,” Prof. Duffy says.
However, Mr Crowe said that while a crown specifically may not rest in the Vatican, there could be some artifact belonging to Brian Boru contained within the Holy See’s reliquary.
Mr Crowe said that when he asked his questions of the Department of Foreign Affairs, he had sought engagement with the Holy See, rather than with historical experts.
“I don’t think the position should be to ask an expert in UCD and if they say it doesn’t exist, then it doesn’t exist,” Mr Crowe said.
He said that the Vatican is unaware of how much treasure is contained within its reliquary, and is particularly seeking for the Holy See to identify how much of it is from Irish sources.
“There’s Irish treasures given to the Vatican. Wouldn’t it be nice to know what ancient items were gifted to the Vatican,” he added.
In particular, Mr Crowe said that, if possible, some of the relics should be returned to Ireland to allow them be put on display, rather than sitting in the Vatican’s reliquary.