Joe Biden is projected to win the election and become the 46th president of the United States.
After a nail-biting race, the Democratic candidate took an unbeatable lead in Pennsylvania - picking up its 20 Electoral College votes and past the 270 needed to gain the White House.
It makes Donald Trump, who is currently at one of his golf clubs in Virginia, the first one-term president since 1992, when George HW Bush failed to clinch four more years.
Celebrations broke out on the streets in Washington DC, New York and Pennsylvania, with people dancing and cheering and one jubilant American declaring: "We made history."
Mr Trump refused to concede the election and in a written statement released by the campaign accused his opponent of "rushing to falsely pose as the winner".
"Beginning Monday, our campaign will start prosecuting our case in court to ensure election laws are fully upheld and the rightful winner is seated," he added.
"I will not rest until the American people have the honest vote count they deserve and that democracy demands."
But three days and 16 hours after the first polls closed, president-elect Mr Biden has accepted victory and announced in his first public comments that "democracy beats deep in the heart of America".
"With the campaign over, it's time to put the anger and the harsh rhetoric behind us and come together as a nation," he said.
"It's time for America to unite. And to heal. We are the United States of America. And there's nothing we can't do, if we do it together."
Mr Biden's path to power looked in doubt when he failed to make early, convincing gains in areas like Ohio, Texas and Iowa.
And while counting continued, Mr Trump made incendiary claims about ballot stuffing and accused his opponents of "fraud" - without providing any evidence.
He even tried to claim victory early, declaring in an address to the nation from the White House: "We will win this and as far as I'm concerned we already have won it."
But Mr Biden, who will be the oldest sitting president ever, urged supporters to "keep the faith" and wait until all votes had been counted.
As the hours wore on, Mr Biden finally started gaining ground - and flipped the first red state to blue in Wisconsin.
The Trump campaign immediately demanded a recount due to "reports of irregularities", and launched legal action to try to halt counting in Pennsylvania.
But Mr Biden hit back, telling him: "We the people will not be silenced; we the people will not be bullied; we the people will not surrender."
The former vice-president to Barack Obama also said "it is clear" he was on course to win, having clinched bigger margins in crucial swing states than Mr Trump won them by in 2016.
Mr Trump has said he may contest Mr Biden's White House win in the Supreme Court.
Analysis: How Joe Biden paved his path to power - and what comes next for divided America
By Cordelia Lynch, US correspondent
Joe Biden has done what Democrats nominated him to do - win back the Rust Belt to win back the White House.
He did it by getting back the white voters who deserted the Democratic Party four years ago.
Among them, some of the non-college educated voters that couldn't find it in themselves to vote for Hillary Clinton.
But much more critical to his success were the college educated voters in the suburbs and densely populated cities; Mr Biden is the beneficiary of demographic change.
Back in March in the South Carolina primary, it was black voters that helped secure his nomination when he was struggling.
Eight months later, it is black voters in Philadelphia, Detroit and Milwaukee who have helped push him over the line once again.
With it, Mr Biden achieved something monumental - more votes than any presidential candidate in US history, passing the 69.4 million record that Barack Obama set in 2008.
At a time of unprecedented discord, his call for unity, stability and civility resonated.
But it wasn't a landslide and while Democrats retain control of the House they suffered some critical losses.
The control of the Senate also hangs in the balance. Without it, passing legislation will be very, very challenging.
Can bi-partisan Mr Biden work with the other side in such a divided climate? The answer to that will define his presidency.
