Representatives from across the political spectrum were united in grief as they stood for a minute's silence in solidarity with the victims of the Manchester terror atrocity.
The Dáil fell silent as TDs paid their respects to the victims of the bombing at the Manchester Arena that left at least 22 people dead and 59 injured, many of them children.
Taoiseach Enda Kenny said the hearts and thoughts of all Irish people were with the people in Manchester stricken by this horrific terror.
"Those parents who had the privilege to bring children to a concert such as this will know that the excitement goes on for months," Mr Kenny said.
The Taoiseach said Ireland kept monitoring the threats of terrorism and the authorities were continually vigilant.
Earlier, President Michael D Higgins offered his sympathy on behalf of the Irish people in what he called an "appalling attack".
He will write a formal letter to Queen Elizabeth and Manchester Mayor Andy Burnham to convey "the sympathy of the Irish people".
"Manchester has been home to the Irish and so many nationalities for centuries and at this terrible time I want to send the people of this great and welcoming city not only our sympathy but our solidarity."
Social Protection Minister Leo Varadkar said it was any parents' worst nightmare.
"It was a cowardly act, an attack on innocence, on children. And I think anyone who is a parent who's dropped their daughter off at a concert or a big brother who dropped a sister to a concert, you worry about them, but you always think that things are going to be okay and you expect that they'll come home.
On this occasion, some people didn't. So certainly my thoughts and prayers are with everyone in that city," he told RTÉ's Primetime.
Tánaiste and Justice Minister Frances Fitzgerald also offered her sympathies, noting the close ties between Ireland and the people of Manchester.
Her views were echoed by Foreign Affairs Minister Charlie Flanagan, who said: "I am shocked and horrified by the large loss of life in Manchester last night and my thoughts and prayers are with those affected, and we stand by our nearest neighbour, the UK especially due to the strong links between our country and the city of Manchester."
Fianna Fáil leader Michéal Martin described it as a "barbaric attack on innocence".
"As a parent, I find this attack exceptionally difficult to comprehend, and while details are limited at present, it's clear that whoever orchestrated this attack cares little for basic decency and humanity," he added.
Archbishop of Armagh Eamon Martin offered prayers to the victims and their families and sent his condolences to Bishop of Salford John Arnold.
Meanwhile, books of condolence are being opened across the country in solidarity with the people of Manchester.
Dublin Lord Mayor Brendan Carr will open a book of condolence at 4pm today at the Mansion House in Dublin on behalf of the people of Dublin.
Meanwhile, President Donald Trump has expressed his "deepest condolences" to the victims of the Manchester bombing calling the attackers "evil losers".
The US president was speaking in Bethlehem during his trip to the Middle East. Other leaders from around the world also condemned the terror attack.
Australian Prime Minister Malcom Turnbull told the country's parliament the incident was a "brutal attack on young people everywhere".
Canadian Prime Minister Justin Trudeau tweeted: "Canadians are shocked by the news of the horrific attack in Manchester. Please keep the victims & their families in your thoughts."
Ariana Grande had just finished the final song of her sell-out concert, and excited children clutching giant pink balloons or wearing kitten ears - Grande's trademark - were filing out of the Manchester Arena with parents eager to get them home to bed.
For Britain's security agencies, London always seemed like the likely target. For years, the capital of 8 million with hundreds of thousands of weekly tourists and dozens of transit hubs had prepared for and feared a major terror attack.