Barack Obama was on course to make history tonight by becoming the first black president of the United States.
Millions of Americans today joined long queues around the country as they prepared to vote for a new era in US politics.
A record high turnout of 130 million people were expected to vote for the 44th president of the United States, with 30 million having already cast their ballots.
Front runner Obama, who appeared to wipe tears from his cheeks on the campaign trail yesterday following the death of his grandmother, joined the nation's earliest voters today in Chicago.
His Republican rival John McCain plans to vote later in Arizona.
After one of the longest and most expensive presidential elections in history the nation will elect either its first black president or its first female vice president, Republican Sarah Palin.
Both candidates were planning last-minute campaign stops to try to woo any Americans still undecided after a hard-fought almost two-year campaign which is estimated to have cost £1.5 billion.
"I voted," Mr Obama told reporters as he held up the validation slip he was handed after turning in a ballot at his Chicago neighbourhood's precinct of Hyde Park.
The 47-year-old Illinois senator was accompanied by his wife Michelle and their two young daughters Malia, 10, and Sasha, seven.
He will end his campaign late tonight at a rally in Chicago where an estimated one million people are expected.
In his final rally in Virginia, which has not voted for a Democratic presidential nominee in 44 years, he told almost 100,000 people: "I'm feeling kind of fired up. I'm feeling like I'm ready to go.
"At this defining moment in history, Virginia, you can give this country the change it needs."
Obama campaign manager David Plouffe said he was confident that new voters and young voters would fuel an enormous turnout to benefit the Democrat.
"We just want to make sure people turn out," Mr Plouffe told NBC's Today show.
"We think we have enough votes around the country."
Mr Obama led by almost eight points in the latest average of national polls by RealClearPolitics.com but Mr McCain remained hopeful of a surprise victory.
"I think these battleground states have now closed up, almost all of them, and I believe there's a good scenario where we can win," he told The Early Show on CBS.
"Look, I know I'm still the underdog, I understand that.
"You can't imagine, you can't imagine the excitement of an individual to be this close to the most important position in the world, and I'll enjoy it, enjoy it. I'll never forget it as long as I live."
Americans will decide between Mr Obama, an inexperienced senator with a powerful message of change and hope for the nation, and former Vietnam prisoner of war Mr McCain, who, at 72, would be the oldest first-term president with 26 years of experience in the US Congress.
But it was a bitter-sweet day for Mr Obama whose 86-year-old grandmother Madelyn Dunham, who helped raise him and was frequently mentioned at key points in the race for the White House, died of cancer on Sunday night.
It is "one of the most important elections in the history of the country and the history of the world," Professor Allan Lichtman of the American University in Washington DC said.
The next president will have to face "perhaps the greatest financial crisis since the Great Depression", two wars in Iraq and Afghanistan, and "one of the gravest challenges in the history of mankind - catastrophic climate change".
Mr Lichtman also said today's election would herald a "sea change" in America's relationship with the world as it moved from a primarily unilateral approach under George Bush to a multilateral one.
He said Mr Obama was "the most significant breakthrough candidate in all American history".
"He could do for race in America what John F Kennedy did for religion in America," he said.
"Kennedy governed as a president of all America, proving that a (Roman) Catholic would not be a Catholic president, but a true American president.
"And ever since then the issue of Catholicism has been non-existent."
He went on: "If Obama wins and Obama governs as the president of all Americans, as I'm confident he will, he can do to the issue of race the same kind of transformations that John F Kennedy achieved for the issue of Catholicism in 1960."
Later, Prime Minister Gordon Brown said the campaign had been "historic" - but stuck with convention by refusing to say whom he wanted to win.
"That is for the American people to decide and we will have the result very soon," he said during his tour of the Gulf.
"What I do know is that American leadership is going to be very important in the next critical time and I look forward to working with the next president whoever he is.
"I think whatever the result of the American election... history has been made in this campaign - the women coming to the fore, a black candidate coming to the fore. But it is for the American people to decide, it is their decision."