Democratic rival Hillary Clinton has conceded to the billionaire businessman as the world's financial markets react to the uncertainty over him with heavy losses.
Opinion polls had increasingly pointed to an inevitable win for Hillary Clinton, but Donald Trump has done what seemed impossible and will be the next United States president.
Mr Trump and his family greeted a cheering sea of red hats at his campaign headquarters in New York before calling for unity on national television.
"Now it's time for America to bind the wounds of division. We have to get together. To all Republicans and Democrats and independents across this nation, I say it is time for us to come together as one united people."
He says the victory was the victory of a movement.
"Ours was not a campaign but, rather, an incredible and great movement made up of millions of hard-working men and women who love their country and want a better, brighter future for themselves and for their family."
Mr Trump says he will keep his promise to "Make America Great Again."
"We have a great economic plan. We will double our growth and have the strongest economy anywhere in the world. At the same time, we will get along with all other nations willing to get along with us."
But while excitement reigns around the Trump camp, financial markets around the world see it differently.
As votes were tallied, markets responded minute by minute and now reflect the fear and uncertainty surrounding the presidency of a man who has never held public office.
The response resembles that after the Brexit vote in July, in which Britain decided to leave the European Union.
A US citizen living in France, Andy Roughton, tried to explain the vote in his homeland, saying it reflects an attitude change.
"Probably the biggest lesson is that America is just tired of corruption in government, and they want somebody to go in there who's not linked to anybody else, just his own self. And I think that every government has people that are pushing their political agenda, and I just think that's not good for the people."
Arizona Republican senator John McCain, re-elected to his sixth term, says he looks forward to the challenges after a tough campaign.
"This has been a difficult national election and not always an uplifting one. But Americans have done their duty as citizens and chosen a new president. For too long, Washington has schemed and fought and manoeuvred to gain political advantage at the cost of delivering for the American people. We've made too little of any progress meeting the great challenges of our time, which are many and difficult."
Early Republican presidential candidate Marco Rubio, who also returns to the senate, offered hope.
"I hope that I and my colleagues, as we return to work in Washington DC, can set a better example of how political discourse should exist in this country. And I know people feel betrayed, and you have a right to."
Vermont senator Bernie Sanders, beaten out for the Democratic nomination by Ms Clinton, says the Trump campaign has relied on division when the country needs unity.
"When you have a campaign like Mr Trump's, where the cornerstone of this campaign is based on bigotry and trying to divide us up, I think that's very bad for our country. And I think we have somebody who even questions the very fabric of our democracy and says, 'Well, I'll accept the election if I win, but, if I lose, I may not.' That's not what democracy is about."
US ambassador to Japan Caroline Kennedy, the daughter of former Democratic president John F Kennedy, says she wants a president who reflects the nation.
"The America that I know deserves a president who stands for tolerance, inclusion, diversity, respect for human rights, the rule of law and a commitment to those who are often left out of the solutions: women, children, the less fortunate. The America I know deserves a president who embraces our immigrant heritage and is committed to work with our friends and allies around the world to bring hope and opportunity and to work for peace."
Some critics are labelling the controversial decision by FBI director James Comey to reopen the investigation into Ms Clinton's emails as the deadly blow to her campaign.
The review has not changed the agency's conclusion that no charges are warranted, but House Minority Leader Nancy Pelosi says his decision helped Mr Trump.
"When the director of the FBI, Mr Comey, released that letter two Fridays ago, he became the leading Republican political operative in the country, wittingly or unwittingly."
Celebrated US feminist Gloria Steinem says the way Republicans attacked Ms Clinton on her greatest strengths was painful.
"The Republicans arrived at a tactic for John Kerry that now they've pursued, which is ... before that, you generally attacked a candidate for their weakness. They attacked for the strength. So the very fact that ... I mean, in his case, it was that he was a war hero, so they tried to undermine the fact of his heroism. In Hillary's case, every fact-checking service says that she is way the most honest and the most accurate. So they went after her as 'Crooked Hillary' and dishonest and so on, which is so painful."
