President Barack Obama said Ireland and the US are bound by “history, affection and bonds of friendship".
Addressing a crowd of approximately 28,000 people at College Green in Dublin this evening, Mr Obama said never has a nation so small inspired so much in another.
"Irish blood is spilled on our battlefields...Irish sweat built our cities...there's always been a little green behind the red, white and blue."
"An American does not require Irish blood because the two countries are bound by history, affection and bonds of friendship."
To rousing cheers he introduced himself as: “Barack Obama, of the Moneygall O’Bamas. I am here to find the apostrophe that we lost along the way”.
He also paid tribute to former taoiseach Dr Garret Fitzgerald, who died last week.
On the current economic crisis facing the country, Mr Obama said Ireland had faced trials before which it had endured and overcome. "We're people, the Irish and the Americans, who never stop imagining a brighter future."
"This little country that inspires such great things...your best days are still ahead...If anyone tells you otherwises, remember the simple mantra, Is féidir linn. Yes we can," the US president said in conclusion.
The speech was the final official engagement of his visit to Ireland and the president is expected to cut short his visit and depart from Dublin airport this evening.
The early departure is based on fears that an ash cloud from the erupting volcano in Iceland may force the closure of Irish air space tomorrow and effectively trap him here.
Earlier, the president travelled to Moneygall, Co Offaly by helicopter with his wife Michelle where they were greeted by Mr Obama's cousin Henry Healy and spent about 20 minutes meeting people in the village before visiting his ancestral home.
They then spoke to locals over pints of Guinness in Ollie Hayes' Bar. Mr Obama said "sláinte" before taking a healthy gulp of his drink and insisted that he "always pays his bar tab".
The Obamas spent a few more minutes greeting the crowd gathered in Moneygall before leaving the village shortly before 4.30pm.
Following a meeting earlier today with Taoiseach Enda Kenny at Farmleigh Mr Obama said the bond between the United States and Ireland is not just one of trade and commerce, but carries a “blood lineage”.
The two leaders discussed a range of issues, including the EU-IMF bailout, the banking situation and unemployment.
They also discussed the peace process in Northern Ireland and the consequences of Queen Elizabeth II's visit here last week.
Mr Obama and his wife Michelle arrived in Dublin this morning shortly before 9.30am at Dublin airport and were transferred to the Phoenix Park by helicopter, where they met President Mary McAleese at Áras an Uachtaráin.
Mr Obama then travelled to Farmleigh for a meeting with the Taoiseach. Mr Kenny said the two leaders had discussed issues such as the use of Shannon airport by the US and the role of Irish peacekeepers in Afghanistan.
Speaking after the 40-minute meeting, Mr Obama said he was “extraordinarily grateful” for the welcome he and his wife had received from the Taoiseach and the Irish people. He said the friendship and bond between the United States and Ireland “could not be stronger”.
"Obviously it is not just a matter of strategic interests. It's not just a matter of foreign policy, for the United States and Ireland carries a blood lineage," he said. "For millions of Irish-Americans this continues to symbolise the homeland and the extraordinary traditions of an extraordinary people."
Mr Obama said the US wanted to help strengthen the bonds of trade and commerce between the two countries, and to do everything it could to help Ireland on the path to recovery. “Ireland is a small country but punches above its weight on a range of issues,” he said.
On progress in Northern Ireland, Mr Obama said it spoke “to the possibilities of peace and people in longstanding struggles being able to reimagine their relationships”.
He noted the “mutual warmth and healing” that accompanied the visit of the Queen here last week, which sent a signal not just here in Ireland but around the world, he said. “It sends what Bobby Kennedy once called a ripple of hope.”
Mr Obama paid tribute to all those who had “worked tirelessly” to bring about peace in Northern Ireland. The president said he was proud of the part that America had played in getting both sides to talk and to provide a space for that conversation to take place.
Mr Obama is the sixth US president to make an official visit to Ireland during his period of office, beginning with John F Kennedy in June 1963. Richard Nixon visited in 1970, Ronald Reagan came in 1984, Bill Clinton was here three times between 1995 and 2000 and George W Bush visited in 2006.
