Former Secretary of State Hillary Clinton congratulated Biden and said his election was a "repudiation of Trump".
Nevada Governor Steve Sisolak congratulated Biden and Harris.
President Trump hot has not conceded the race and has vowed to fight the count in court.
"We all know why Joe Biden is rushing to falsely pose as the victor, and why his media allies are trying so hard to help him: they don't want the truth to be exposed", the statement read, as Americans take to the street to celebrate Trump's defeat. "You're going to be the next president of the United States".
Joe Biden is the oldest President-elect in history and Kamala Harris will be the next Vice-President.
"The relationship between our two countries is strong, and I look forward to developing even closer relations with the incoming Biden Administration", Ardern said.
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They would have their lowest points tally after seven matches since 1989/90 if they fail to win. We've lost Luke Shaw because of that.
"Welcome back America!" tweeted the mayor of Paris.
Other leaders who sent congratulations included Germany's Chancellor Angela Merkel, Egyptian President Abdel-Fattah el-Sissi, Indian Prime Minister Narendra Modi, who'd been known for public displays of bonhomie with Trump. and British Prime Minister Boris Johnson, a Trump ally.
The Democrats won in Pennsylvania which means they have 273 Electoral College votes.
"We want to work in our cooperation for a new trans-Atlantic beginning, a New Deal". "Legal votes decide who is president, not the news media", it continues.
Biden replaced the phrase "senator, vice president" in his Twitter account definition with "the president-elect".
In another tweet, PM Modi also congratulated Kamala Harris saying her victory is "a matter of huge pride not just for your chittis, but also for all Indian-Americans".