Former secretary general at the Department of Foreign Affairs Dermot Gallagher has died.
Mr Gallagher - who hailed from Carrick-on-Shannon in Co Leitrim - had spent 40 years in diplomatic service.
He also held a number of senior positions in government departments.
In his career, Mr Gallagher had an influential role in the Northern Ireland peace process.
Former junior minister and former senator Martin Mansergh paid tribute to Mr Gallagher.
He told RTÉ's Marian Finucane programme that Mr Gallagher had as "emollient style of negotiation and diplomacy".
Saddened by the passing of former DFAT SG, Dermot Gallagher. He will be remembered as a distinguished diplomat & for his key role in the GFA— Charlie Flanagan (@CharlieFlanagan) January 15, 2017
RIP Dermot Gallagher ex Irish Ambassador to the US who played a big part in the Peace Process in the early 90's. A true gentleman.— Ken Murray (@NewsMurray) January 15, 2017
Dermot Gallagher RIP was a brilliant, creative and warm human being and diplomat. I was honoured to call him my friend— Ray Bassett (@ray_basssett) January 15, 2017
Michael D Higgins said Mr Gallagher "dedicated a lifetime to public service, serving with distinction as ambassador to the United States and making a significant contribution to the peace process in Northern Ireland".
"Sabina and I send our deepest condolences to his family, friends and former colleagues at this sad time," he said.
"I have learned with great sorrow of the passing of Dermot Gallagher, a former Secretary General of my Department who retired in 2009," Minister Charlie Flanagan said in a statement on Sunday afternoon.
"A proud native of Leitrim, Dermot ably served successive Governments with great loyalty and constant commitment. His talented service covered the spectrum of the Department's work from EU affairs to development aid. It included two Ambassadorial posts, in Nigeria and later in the US.
"However, perhaps it was in the area of Northern Ireland and the peace process that Dermot made his greatest contribution. As a young diplomat, he was part of the Government's negotiating team at the Sunningdale talks in 1973 and many years later he was a major figure in the negotiation of the Good Friday Agreement. As Secretary General of the Department, he also prioritised a focus on providing practical support to Irish citizens abroad.
"Dermot will be greatly missed by his many friends and colleagues in my Department, in the GAA to which he also made a huge contribution and in County Leitrim. I extend my deepest sympathy to his wife Maeve and to Dermot's children Fiona, Aoife and Ronan. Ar dheis Dé go raibh a anam."