Joe Biden has received a standing ovation from MPs in Dublin and told them he wished he could extend his stay in Ireland, in a speech he called "one of the great honours of my career".
The US President on Thursday hailed a "partnership for the ages" between Ireland and America as he addressed parliament on a tour celebrating his Irish ancestry.
"I'm at home," Mr Biden said. "I only wish I could stay longer."
On the second day of his trip, Mr Biden met leaders of the Republic of Ireland who have described the visit as a homecoming.
Mr Biden said the family story he mentions so often was "emblematic of the stories of so many Irish and American families".
"They speak to a history defined by our dreams, they speak to a present written by our shared responsibility and they speak to a future poised for unlimited shared possibilities," he said.
"Today I'd like to reflect on the enduring strength of the connections between Ireland and the United States — a partnership for the ages."
Mr Biden is the fourth US president to address Ireland's Parliament after John F. Kennedy in 1963, Ronald Reagan in 1984 and Bill Clinton in 1995.
Irish Taoiseach Leo Varadkar told Mr Biden "you grace us with your presence" as the pair held closed-door talks before the speech.
They praised each other's response to the war in Ukraine. Mr Varadkar praised America's partnership with European allies, while Mr Biden saluted militarily neutral Ireland for taking in refugees from the conflict.
The Taoiseach said he was delighted to have Mr Biden staying for so long.
"We’re one of only 200 countries in the world and we’re very fortunate that we’re always high on the president’s agenda," he said.
Joe Biden visits the Republic of Ireland - in pictures
A day after his visit to Northern Ireland to mark 25 years since the Good Friday Agreement, Mr Biden renewed his call for power-sharing in the north to resume.
His speech was watched by key figures from the 1998 negotiations including nationalist leader Gerry Adams and former Irish leader Bertie Ahern.
“There are literally hundreds of American corporations ready to come and invest, but they’re cautious because the institutions are not in place,” he said.
He said the UK “should be working closer with Ireland” to support the north.
Mr Biden earlier met Irish President Michael D. Higgins on a first full day in the Republic of Ireland, replete with nods to his Irish heritage.
He signed a visitors' book with the words: "Your feet will bring you where your heart is." Ringing a peace bell at Mr Higgins's residence, he said: "This is for all my Irish ancestors".
"There are so many Irish-Americans, like my relatives who got to America in 1844, '45, and '46, who've never been back here," he said.
Mr Biden has met distant cousins on his trip, toured a castle near where his ancestors in the Finnegan family once lived and will meet ancestry researchers on Friday.
Crowds have welcomed Mr Biden to the Republic with posters and American flags lining the route of his motorcade.
"The Irish people are very conscious of our strong connection to President Biden," Mr Higgins said.
However, his arrival in Ireland on Wednesday was marred by a gaffe.
Speaking in Dundalk, he mixed up rugby's All Blacks with the Black and Tans, British police reservists known for violently suppressing Irish nationalists in the 1920s.
"You see this tie I have with this shamrock on it? This was given to me by one of these guys right here. He was a hell of a rugby player, and he beat the hell out of the Black and Tans," Mr Biden said.
White House aide Amanda Sloat said it was "incredibly clear" he meant the New Zealand rugby team.
Alluding to the error in a speech on Thursday, Mr Biden made sure to say "All Blacks", drawing laughter from MPs.
The White House also had to fend off claims that Mr Biden was snubbing the UK by spending only half a day in Northern Ireland.
Mr Biden gave a speech at Ulster University after brief meetings with Prime Minister Rishi Sunak and leaders of Northern Irish parties.
The visit was arranged to mark 25 years since the Good Friday Agreement, but the power-sharing government envisaged by the deal has been in limbo for months.
Mr Varadkar said Mr Biden did not want to be "overbearing or interfering" by pushing harder for a return of the Northern Ireland Assembly.
