Air Force One landed amid tight security and wet, blustery conditions at Dublin Airport just after 9.30am.
The President was met by Ireland's deputy prime minister Tanaiste Eamon Gilmore and his wife Carol Hanney, and US ambassador to Ireland Dan Rooney.
Mr Obama is due to call on President Mary McAleese at her residence in the Phoenix Park, Aras an Uachtarain, before holding 45 minutes of talks with Taoiseach Enda Kenny.
The President will then travel to his ancestral home in Moneygall, Co Offaly, ahead of a public concert later in Dublin.
Mr Obama waved as he stepped off the plane with his wife, Michelle.
The visit lacked the ceremony of last week's state visit of the Queen, with only a small welcoming party waiting on the runway apron to greet the President and shake hands.
The Obamas immediately boarded helicopter Marine One to travel the few miles to Aras an Uachtarain.
Airspace around Dublin has been shut down for the President's arrival and transfer over the capital.
President McAleese greeted President Obama at the front steps of the Aras.
"Thank-you so much. We're thrilled to be here," he said.
And despite the grey skies, the President remarked: "The sun's coming out - I can feel it."
He signed the visitor's book before holding private talks in the drawing room of the Aras.
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