Donald Trump will become the 45th US president after a stunning victory over Democrat Hillary Clinton.
The Republican nominee's projected victory came down to a handful of key swing states, despite months of polling that favoured Mrs Clinton.
The battlegrounds of Florida, Ohio and North Carolina cleared the way for his Brexit-style upset.
Global markets plummeted, with the Dow set to open 800 points down.
Mr Trump's victory in Wisconsin put him over the 270 out of 538 electoral college votes needed to win the White House.
The US president-elect took to the stage at his victory rally in New York and said: "I just received a call from Secretary Clinton. She congratulated us on our victory."
"Hillary has worked very long and very hard over a long period of time, and we owe her a major debt of gratitude for her service to our country."
He added: "It is time for us to come together as one united people."
The real estate tycoon, former reality TV star and political newcomer, who was universally ridiculed when he declared his candidacy in June last year, said his victory had been "tough".
Mr Trump has so far won 28 US states, smashing into Mrs Clinton's vaunted electoral firewall in Pennsylvania and Wisconsin, states that have not supported a Republican presidential candidate since 1988 and 1984 respectively.
He also won Iowa, which has not elected a Republican since 2004.
Mr Trump will also take office with Congress fully under Republican control as Democrats were unable to wrest control of the Senate.
Mrs Clinton, 69, has only notched up victories in 18 US states and the District of Columbia.
New Hampshire and Michigan – which had also been expected to fall in the Clinton column – remained too close to call as of Wednesday morning.
The Democratic candidate, who dreamed of becoming the first female US president, did not show up for what was meant to be her victory rally across town in Manhattan.
The mood was dark at her election night party in the Javits Center, as supporters wept and left early.
At Trump headquarters earlier, his fans cheered and chanted about the Democratic nominee: "Lock her up!"
Mr Trump, a populist billionaire, provoked controversy on the campaign trail for comments about women, Muslims and a plan to build a wall along the US-Mexican border.
He fired up white, working-class American voters who were angry at the Washington establishment and felt left behind by globalisation.
On the eve of the vote, Mrs Clinton was ahead by four points in a BBC aggregate of opinion polls, but it was well within the margin of error.
She saw her campaign dogged by FBI investigations into whether she abused state secrets by operating a private email server during her time as US secretary of state.
Last Sunday, the law enforcement bureau cleared her once again of any criminality.
Mr Trump and Mrs Clinton were vying to succeed Democratic President Barack Obama.
After two four-year terms in the White House, he was barred by the US constitution from running for re-election.