The bill for the visits of President Barack Obama and Queen Elizabeth to the Republic was €40 million, almost double the previous estimate.
Several TDs reacted with shock when justice minister Alan Shatter revealed the cost of the "massive garda effort," which accounted for €36 million of the final bill.
It prompted complaints that the security operation was "over-the-top" and that some of the money would have been better spent on reversing financial cutbacks.
But before the Oireachtas Justice Committee, Shatter defended the cost of getting thousands of gardai to provide security for the queen and Mr. Obama.
"The vast scale of the security operation put in place by An Garda Siochana was commensurate with the very real security threats involved," he said.
Mr. Shatter also said there was a risk of enormous damage to the country's reputation if anything had gone wrong during the visits, both of which passed off successfully without any major incidents.
"It is important the cost is balanced against the substantial long-term benefits to the country in terms of favorable press coverage and free advertising, in particular, through the international televised media," he said.
Gardai had all their leave cancelled during the visit and were required to work shifts of up to 18 hours.
But Independent Dublin North Central TD, Finian McGrath, said he felt Mr. Shatter and garda management had mounted an "over-the-top" security operation when only a small number of people posed a threat.