RTÉ has announced that Marian Finucane passed away suddenly today, at home.
Ms Finucane joined the national broadcaster in 1974, where she worked initially as a continuity announcer before becoming a programme presenter.
The 69-year-old won a number of awards for her work, including the Radio Journalist of the Year award in 1988.
Ms Finucane and her partner of more than 30 years John Clarke exchanged wedding vows in January 2015.
The couple had two children together; a son Jack and a daughter Sinead. Eight-year-old Sinead died in 1990 after she developed leukaemia.
Ms Finucane was the original presenter of RTE Radio 1's Live Line programme before she moved to a slot vacated by Gay Byrne in 1999. In 2005, the show moved to weekends.
President Michael D Higgins said it is with great sadness that her learnt of her death, saying Ireland has lost "a deeply respected, trusted and much-loved broadcaster".
President Higgins said: "A superb professional, many will remember the wisdom and sensitivity with which Marian Finucane dealt with discussions and confrontations between different voices on what were controversial issues of the day.
"There will be many, in every part of Irish life, who will miss Marian’s voice, but of course her loss is felt most acutely by her family and friends.
"To her husband John, her son Jack and to all the members of her extended family and wide circle of friends and colleagues Sabina and I express our deepest sympathies.”
The Taoiseach, Leo Varadkar, said he was "stunned and deeply saddened" to hear of Ms Finucane's death.
He said: "She was a true broadcasting legend who reshaped current affairs radio in Ireland. Ireland will miss her voice. Weekend mornings will never be quite the same again.
"I spent many hours in the studio with Marian. She was thorough, courteous and professional. I’m very sad to think that we won’t hear her voice again on the radio.
"The deepest sympathies of the Irish Government to her family, friends and colleagues."
RTÉ presenter Joe Duffy said he was shocked at the news.
He said: "She was always supportive, much at times to my own bafflement, you'd get a phone call from Marian or you'd meet her in the corridor and she'd listen to Live Line every single day because she believed she had to listen to radio every day for a week when she was doing her weekend programme.
"It's a terrible, terrible shocking loss on the second day of 2020, it really is."
Minister for Culture, Josepha Madigan, paid tribute to Ms Finuncane, saying: “I am deeply shocked and saddened to hear of the death of Marian Finucane.
"We have lost another of our most cherished broadcasters. Marian was a strong, inspirational and always thought-provoking journalist."
Former RTÉ broadcaster Pat Kenny paid tribute to Mrs Finucane.
Speaking on Newstalk's Hard Shoulder, he said: "My reaction is total shock... I just found it very, very hard to comprehend that Marian was no longer with us.
"She and I worked hand-in-glove over many years.
"The listener felt, I think, that Marian was asking the question that they wanted answered... her skill was to contrive a question and be surprised at an answer she already knew... sometimes she was just genuinely curious to get an answer from a guest.
"The warmth, the curiosity, the intelligence of Marian Finucane is what people will most recall and cherish."
Dee Forbes, Director General RTÉ, said: “We learned today of the sudden passing of Marian Finucane with profound shock and sadness.
"Marian was a broadcaster of immense capability; a household name, she was first and foremost a tenacious journalist with a zeal for breaking new ground.
"From Women Today to Liveline to her weekday radio show on Radio 1 and, latterly, her enormously popular Saturday and Sunday radio programme, she tackled the big social issues of the day with command and insight.
"Multi-skilled, she forged a distinguished career on television, as well as undertaking significant charity work in Africa.
She had many landmark interviews, among them a searing interview with author Nuala O'Faolain shortly before her death in 2008, in which O'Faolain talked about her experience of facing death.
You can listen back to this interview here.
Moya Doherty, Chair of RTÉ, said: “It is with the deepest shock and sadness that I heard the news of Marian Finucane.
"Marian was a pioneer in women’s broadcasting and was rightly renowned for her fearless yet human interview technique.
"Many who work in broadcasting today, male and female, owe her a great debt. RTÉ has lost another great champion and another great talent, but we are the richer for having known and heard her work.”
Jim Jennings, Director of Content, RTÉ, said: “The work and legacy of Marian Finucane is without parallel in Irish broadcasting. With the committed team on Women Today she tackled issues that were largely uncovered and unspoken.
"On Liveline she templated a phone discussion format uniquely suited to Irish audiences. An award-winning documentary maker, she was an interviewer of profound sensitivity and insight.
"As presenter of RTÉ Radio 1’s flagship weekend morning programme, she had the pulse of the nation. It is with great sadness that we mourn this loss to Irish journalism, and to all her colleagues in RTÉ. But our immediate thoughts are with her family today, at this time of great shock and mourning.”
Tom McGuire, Head of RTÉ Radio 1, said: “Marian Finucane was a defining voice for RTE Radio 1, and for the nation.
"Her work on Liveline was without parallel, where she merged an unsurpassed journalistic vigour with a flair for debate and discussion unmatched among her peers.
"As the voice of weekends, she parsed the stories of the day, tackling big interviews with ease and insight. Her loss is a deep shock to all of us, and our thoughts are with Marian’s family at this time.”