Dermot Gallagher "embodied the best of Ireland and its people", said Taoiseach Enda Kenny in a warm tribute to the former secretary general of the Department of Foreign Affairs, who has died aged 72.
The Taoiseach said Mr Gallagher was "a patriot, an outstanding public servant" who was " intellectually brilliant yet unassuming".
"He had a rare elegance and warmth," said Mr Kenny.
"He used his contacts and authority to do good. He showed immense humanity and compassion to those who needed it most.
"Dermot used to say 'a shroud has no pockets' but there is neither shroud nor pocket big enough to hold even a minuscule amount of his wisdom, decency and kindness.
"Dermot Gallagher is a major loss to Irish public life. Today, Ireland is the less for his passing."
President Michael D Higgins led tributes, saying 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."
Foreign Affairs Minister Charlie Flanagan said: "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.
"Perhaps it was in the area of Northern Ireland and the peace process that Dermot made his greatest contribution."
Tánaiste and Justice Minister Frances Fitzgerald said: "On his retirement. . . he continued his very distinguished career of public service by serving for a number of years as chairperson of the Garda Síochána Ombudsman Commission.
"He combined a deep respect for An Garda Síochána with a determination that all who served in it should live up to its highest standards."
Fianna Fáil leader Micheál Martin said Mr Gallagher was "a true gentleman who epitomised the very essence of public service".
Sinn Féin leader Gerry Adams said he "gave a lifetime of service to the Irish state".
Fr Seán McManus, president of the Washington Capitol Hill-based Irish National Caucus, said: "May God rest Dermot's noble, Leitrim soul."