Michael D. Higgins described the monarch as a "unique, committed, and deeply respected Head of State".
President Michael D. Higgins has led tributes from across the political landscape as Irish leaders react to the death of Queen Elizabeth II.
The British Monarch died at the age of 96 in Balmoral, surrounded by family.
The President expressed "profound regret and a deep personal sadness" having
learnt the news.
"On behalf of the people of Ireland, may I express my heartfelt sympathy to His Majesty the King and to the Royal Family on their very great personal loss," the President said.
"May I offer my deepest condolences to the British people and to the members of the Commonwealth on the loss of a unique, committed and deeply respected Head of State.
"Her Majesty served the British people with exceptional dignity. Her personal commitment to her role and extraordinary sense of duty were the hallmarks of her period as Queen, which will hold a unique place in British history.
"Her reign of 70 years encompassed periods of enormous change, during which she represented a remarkable source of reassurance to the British people. This was a reassurance based on a realism of the significance of present events, rather than any narrow conception of history.
"This was so well reflected by a remarkable generosity of spirit which helped to foster a more inclusive relationship both with the British people themselves and with those with whom her country has experienced a complex, and often difficult, history."
Taoiseach Micheál Martin also
expressed sympathies with the Royal Family on behalf of the Government.
"The Queen’s reign was one of historic duration, immense consequence and a focus of respect and admiration around the world," Martin said.
"Her dedication to duty and public service were self-evident and her wisdom and experience truly unique.
"The Queen’s passing is indeed the end of an era. Her State Visit to Ireland in 2011 marked a crucial step in the normalisation of relations with our nearest neighbour.
"That visit was a great success, largely because of the many gracious gestures and warm remarks made by the Queen during her time in Ireland."
Sinn Féin Leader Mary Lou McDonald said that the Queen's passing marked "the end of an era."
"Relationships between our two countries for so long marked by conflict and suffering have been recast and reimagined through the Good Friday Agreement.
"The Queen proved a powerful advocate and ally of those who believe in peace and reconciliation.
"I salute her contribution to the huge change that has evolved in recent years.
"Her death is a moment of heartbreak and pride for the British people. To them, and especially to Irish unionists, I extend on behalf of Sinn Féin and Irish Republicans sincere condolences.
"Ar dheis Dé go raibh a hanam dilis."
