Biden, who was Barack Obama’s former Vice President, became the president-elect after taking the swing state of Pennsylvania, several US news outlets have projected.
He is currently leading the election by 273 electoral votes, but could win on a stronger foot if Nevada and Arizona stay blue.
The president-elect will be joined in office by Kamala Harris, who goes on to aid the Democratic party as the Vice President of the United States.
His wife, Jill Biden, will also be by Joe’s side in Washington D.C., as she has been since the couple tied the knot on June 17, 1977.
Biden promised to be a "President for all Americans" after winning the election.
He tweeted: "America, I’m honoured that you have chosen me to lead our great country.
"The work ahead of us will be hard, but I promise you this: I will be a President for all Americans — whether you voted for me or not.
"I will keep the faith that you have placed in me."
Crowds celebrated in the streets of Philadelphia after the result was announced.
Kamala Harris said: "This election is about so much more than @JoeBiden or me.
"It’s about the soul of America and our willingness to fight for it. We have a lot of work ahead of us. Let’s get started."
Donald Trump was playing golf when he was told he lost, according to MSNBC columnist Liz Plank.
Prime Minister Boris Johnson congratulated the new president and said the UK will work "closely together" with the US.
He tweeted: "Congratulations to Joe Biden on his election as President of the United States and to Kamala Harris on her historic achievement.
"The US is our most important ally and I look forward to working closely together on our shared priorities, from climate change to trade and security."
Biden won the majority in 23 states in America, with his strongest lead in California, where he had over 65% of the public vote.
The Democrats also secured the entire of the west coast, including Washington, Oregon and Nevada.
Adjoining Arizona, New Mexico and Colorado also voted for the 2020 Biden and Harris campaign, as well as Hawaii.
On the east coast, Joe Biden scooped Maine, Rhode Island, Vermont, Massachusetts, New York, New Hampshire and New Jersey.
Delaware, the District of Columbia and Virginia turned blue too, as well as Minnesota, Wisconsin, Illinois and Michigan.
Trump won most middle America states, including Montana, Idaho, Utah, Texas, Wyoming, North Dakota, South Dakota, Nebraska, Oklahoma, Kansas, Arkansas, Louisiana, Iowa and Missouri.
He also won Mississippi, Kentucky, Indiana, Ohio, Florida, South Carolina and West Virginia.
Votes are not yet in for North Carolina, but Trump is projected to also take the state with a majority lead of over 50%.
But reacting to the announcement, Trump warned the election is 'far from over'.
He is likely to seek legal action after he accused, without proof, several states of electoral voter fraud.
In a statement, he said: "The simple fact is this election is far from over.
"Joe Biden has not been certified as the winner of any states ... Beginning Monday, our campaign will start prosecuting our case in court to ensure election laws are fully upheld and the rightful winner is seated."
Hillary Clinton, who lost to Trump in 2016, said Biden's win was a "repudiation of Trump".
She tweeted: "It's a history-making ticket, a repudiation of Trump, and a new page for America.
"Thank you to everyone who helped make this happen. Onward, together."
It is the first time in 28 years an incumbent US president has failed to secure a second term in the White House.
As the gap narrowed between the current U.S. president and Joe Biden, Trump urged his voters to stop the vote.
He also filed lawsuits in Georgia, Nevada, Pennsylvania and Michigan, and is seeking a recount in Wisconsin.
The new suit in Nevada is claiming thousands who voted were out of state residents, a claim the Trump administration lodged without proof.
Team Biden said the lawsuits were designed to drive a “false narrative” to undermine the results as it became clear Biden would be knocking Trump off of the top seat.
Labour leader Sir Keir Starmer congratulated Joe Biden on his projected victory.
He tweeted: "He ran a campaign on the values that we in the United Kingdom share – decency, integrity, compassion and strength.
"And I want to congratulate @KamalaHarris on being elected Vice-President, the first woman of colour to take that role.
"Their victory is one for hope and unity over dishonesty and division. Millions of Americans of all backgrounds and ages have come together to vote for a better, more optimistic future."
Nicola Sturgeon, the First Minister of Scotland, tweeted her congratulations.
Mark Drakeford, the First Minister of Wales, also sent his congratulations, adding: "Look forward to working with you to build on the strong links between Wales and USA."