Mr Ahern will then hold his last meeting with President George W Bush in the White House. He steps down next Tuesday.
Family, friends and supporters have been flying into Washington in the past couple of days.
Mr Ahern arrived into Andrews Air Force Base late last night, after attending his final cabinet meeting in Dublin.
At 11am local time today (4pm Irish time), he will become the sixth Irish leader to address the Houses of Congress, following presidents Sean T Ó Ceallaigh in 1959, and Eamon de Valera in 1964, taoisigh Liam Cosgrave in 1976, Garret FitzGerald in 1984 and John Bruton in 1996.
He will become just the fifth person to address both Congress and the British Houses of Parliament, following his speech to the latter in May last year.
In doing so, he follows Nelson Mandela, Francois Mitterand, Charles de Gaulle, Haile Selassie I and Nicolas Sarkozy.
The speech will be televised live on RTÉ 1.
The Government remained tight-lipped about the contents of the speech last night, although it previously said it was likely to cover issues such as the peace process, the economy, and US investment in Ireland.
Mr Ahern himself told reporters last Sunday that, in contrast to his Westminster speech, which discussed the Anglo-Irish relationship down through the centuries, the address to Congress would be about the present.
“It’s not going to be about history. It’s going to be about now,” he said.
Following the address, Mr Ahern will attend a special lunch hosted by Congressman Richie Neal, chairman of the Congressional Friends of Ireland.
He will then depart for his final meeting with President Bush in the Oval Office. Essentially a courtesy call, the visit will be brief and no policy issues will be discussed, according to the Government.
Later tonight, Mr Ahern will attend a function in his honour at the Irish embassy in Washington.
DURING today’s lunch, Mr Ahern will present the Congressional Friends of Ireland with a sword which belonged to the Young Irelander, Thomas Francis Meagher.
Meagher, born in Waterford in 1823, opposed British rule in Ireland and in 1848, following a visit to Paris where he witnessed the latest French revolution, presented a tricolour of green, white and orange to a meeting of nationalists in Dublin.
That year, Meagher was convicted of sedition and exiled to Van Diemen’s Land. He escaped to the US in 1852 and served with the Fighting 69th Regiment of the New York Militia before forming the Irish Brigade.
During his visit here in 1963, President John F Kennedy presented the Irish people with a flag of the Fighting 69th, which is now displayed in Leinster House. By presenting the sword today Mr Ahern will be “closing the circle“, a spokesman said.