Barack Obama is set to address US Democrats at the party's national convention, a day after being chosen as their candidate for the White House.
Mr Obama, the first African-American to be nominated for president by a major US party, will formally accept his historic candidacy in Denver, Colorado.
On Wednesday, he was resoundingly endorsed by ex-President Bill Clinton.
Mr Obama's speech comes on the 45th anniversary of Martin Luther King's historic "I have a dream" address.
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Hours before her husband publicly gave Mr Obama his unequivocal backing at the convention, in a moment of high drama his defeated rival Hillary Clinton cut short a roll-call vote to endorse Mr Obama's candidacy by acclamation.
Coronation grandeur
Former Vice-President Al Gore is also due to speak on Thursday, along with Democratic National Committee Chairman Governor Howard Dean, but the focus will be on Mr Obama.
His much-anticipated speech, scheduled for 2015 (0215 GMT), will be the highlight of the party's carefully choreographed four-day convention.
It is likely to have all the pomp and grandeur of a coronation, says the BBC's Matthew Price at the Denver Bronco's stadium.
It is only four years since the would-be president gave a headline-making speech at the previous Democratic Convention.
Questions remain as to whether Mr Obama can cement his standing within his own party, and reach out to those parts of the electorate that are yet to be convinced by him, our correspondent notes.
'New approach'
Mr Obama made a surprise appearance on stage on Wednesday after his running mate, Senator Joe Biden, accepted his own nomination for vice-president in a speech that was sharply critical of the Republican candidate, John McCain.
"We want to open up this convention to make sure that everybody who wants to come can join in the party, and join in the effort to take America back," he said.
Mr Biden stressed the need for a new approach to help Americans struggling to make ends meet and to change US foreign policy in the rest of the world.
The 65-year-old foreign policy expert was chosen as vice-presidential candidate by 47-year-old Mr Obama partly on account of his experience.
Clinton factor
In an address that was bound to be closely scrutinised for signs of discord, Bill Clinton, the last Democratic president, struck a firmly conciliatory note and stressed that he believed Mr Obama was ready to be president.
He said he was proud of his wife, Hillary - who had battled Mr Obama for the Democratic nomination - but that her supporters should now back Mr Obama.
"Barack Obama is ready to honour the oath to preserve, protect and defend the Constitution," said Mr Clinton. "Barack Obama is ready to be president of the United States."
In American political parlance Mr Clinton "delivered", and may now find himself playing a higher-profile role in the campaign to come, says the BBC's Kevin Connolly in Washington.
Earlier, Mrs Clinton had halted a roll call vote - in which each state, in alphabetical order, declares how many votes were cast for each candidate in the primaries - to call for Mr Obama's nomination by acclamation.
In a powerful show of unity, she said: "Let's declare together in one voice, right here, right now, that Barack Obama is our candidate."
The presidential election on 4 November will pit Mr Obama against Mr McCain, who will be nominated next week at his party's convention in Minneapolis-St Paul.
The Republican senator has said he has chosen his vice-presidential candidate, and US media reports the running partners will appear together at a 10,000-strong rally in the swing state of Ohio on Friday.
(BBC)
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