Barrister and political commentator Noel Whelan has died aged 50 after a short illness.
Originally from Co Wexford, the former Fianna Fáil adviser died yesterday evening.
He was a leading figure in the campaigns to introduce same-sex marriage and repeal the Eighth Amendment.
His wife Sinéad McSweeney said: "We are devastated and heartbroken to lose Noel so suddenly ... we are strengthened and sustained by the tributes and kindness. He was our rock and is now our North Star. May he rest in peace."
President Michael D Higgins expressed his "deepest condolences" to Mr Whelan's family, saying he was a driving force in some of the most political campaigns of recent times.
In a statement, President Higgins said Mr Whelan "ever mindful, and proud, of his roots in Wexford" founded the Kennedy Summer School, "which continues to make a lasting contribution to our collective understanding of Irish-American history and relations".
President Higgins said: "I was delighted to accept his invitation to speak at it last autumn and experienced the warmth and generosity he showed to both speakers and audience, and the ease with which he merged matters of Irish, American and Wexford history.
"He did so by having the significant anniversaries of each of these histories celebrated in a most thoughtful way."
Taoiseach Leo Varadkar also paid tribute to Mr Whelan saying that although they came from different party backgrounds, "I feel this morning like Ireland has lost a friend".
We are devastated and heartbroken to lose Noel so suddenly. It isn't possible to reply to each message right now but know that we are strengthened and sustained by the tributes and kindness. He was our rock and is now our North Star. May he rest in peace.https://t.co/YyjT74NnKg— Sinéad McSweeney ☂🦉 (@smcs) July 11, 2019
So sad to hear that Noel Whelan has passed away. We come from different party backgrounds but I feel this morning like Ireland has lost a friend. Such a sharp intellect. So articulate and effective on marriage equality.— Leo Varadkar (@LeoVaradkar) July 11, 2019
Fianna Fáil leader Micheál Martin described Mr Whelan as a man "with a sharp intellect".
In a statement, Mr Martin said: "[He was] never afraid of tackling controversial issues or criticising positions of any political party.
"He understood and knew every constituency and local electoral area across the country and could, off the top of his head, remember quotas from an election held back in the 80s.
"He was a diligent political advisor to Tom Kitt, who was Minister of State for EU affairs from 1992-94 and Noel himself ran for Fianna Fáil in both a Dáil and Seanad election.
"As well as working as a barrister he managed to lead and be very active in the Seanad, Marriage Equality and Eighth Amendment referendums."
Minister for Children and Youth Affairs Katherine Zappone described her "very close friend" as "a man of enormous talent and capacity".
Minister Zappone described Mr Whelan as "an incredible strategist and dynamo" who used his campaigning skills to help to win the Marriage Equality referendum.
She said he was "a change agent" and she worked with him first on the Democracy Matters campaign to save the Seanad.
Minister Zappone said Mr Whelan was an extraordinarily grounded, humble man and a family man, and from those roots he learned how to listen to all points of view and she said he was always willing to change his mind and also willing to step up to the plate.
Tributes were also paid to Mr Whelan in the Dáil.
Tánaiste Simon Coveney said he was somebody who was deeply respected across the political divide.
He said Mr Whelan was an accurate and respected commentator for many years, and dying at the age of 50 was a tragedy for his family.
Fianna Fáil's Dara Calleary said Mr Whelan was very passionate about democracy and about people understanding it.
He said Mr Whelan was exceptionally proud of the history of the country and was never afraid to challenge that potential.
Labour Leader Brendan Howlin said he was shocked to hear about Mr Whelan's passing. He said Mr Whelan was someone with great intellect and incisiveness whose views you listened to.
Mr Whelan is survived by his wife Sinéad and son Séamus.