US Vice President Kamala Harris has said she was honoured to have President Joe Biden's endorsement as the nominee of the Democratic party for the presidential election and asserted that her aim was to unite the nation in "defeating Donald Trump and his extreme Project 2025 agenda".

Her remarks came after Biden (81), in a stunning decision, on Sunday announced that he was withdrawing from the race to be the next president in 2024 and endorsed Harris, who is of both Indian and African origin, as the Democratic Party's new nominee.

Biden's decision to nominate Harris (59) follows weeks of intense pressure from fellow Democrats after his disastrous presidential debate performance against his Republican rival and former US president Donald Trump last month.

"I am honoured to have the President's endorsement and my intention is to earn and win this nomination," said Harris, who has been serving as US' first female, first Black and first South Asian vice president since 2021.

Though Biden's endorsement almost seals her position as the presidential nominee of her party, she still needs to get elected by the party's delegates during the Democratic National Convention in Chicago next month.

Harris immediately secured the endorsement of former president Bill Clinton, thus making it a bit easier for her to win the delegate battle during the Democratic National Convention in Chicago beginning August 19.

"On behalf of the American people, I thank Joe Biden for his extraordinary leadership as President of the United States and for his decades of service to our country," she said.

Harris said over the past year, she has travelled across the country, talking to Americans about the clear choice in this momentous election.

"And that is what I will continue to do in the days and weeks ahead. I will do everything in my power to unite the Democratic Party -- and unite our nation-- to defeat Donald Trump and his extreme Project 2025 agenda... We have 107 days until Election Day. Together, we will fight. And together, we will win," she said.

Former President Bill Clinton and former Secretary of State Hillary Clinton quickly endorsed Harris to be the nominee. "We've lived through many ups and downs, but nothing has made us more worried for our country than the threat posed by a second Trump term," they said in a joint statement.

"He has promised to be a dictator on day one, and the recent ruling by his servile Supreme Court will only embolden him to further shred the Constitution. Now is the time to support Kamala Harris and fight with everything we've got to elect her," the Clintons said.

In her statement, Harris thanked Biden on behalf of the country's people for his extraordinary leadership and said, "His remarkable legacy of accomplishment is unmatched in modern American history, surpassing the legacy of many Presidents who have served two terms in office." "It is a profound honour to serve as his vice president, and I am deeply grateful to the President, Dr Biden, and the entire Biden family. I first came to know President Biden through his son Beau. We were friends from our days working together as Attorneys General of our home states," she said.

"As we worked together, Beau would tell me stories about his dad. The kind of father and the kind of man he is. And the qualities Beau revered in his father are the same qualities, the same values, I have seen every single day in Joe's leadership as President: His honesty and integrity. His big heart and commitment to his faith and his family. And his love of our country and the American people," Harris said.

With this selfless and patriotic act, President Biden is doing what he has done throughout his life of service: putting the American people and the country above everything else, she added.

Earlier, Biden announced that he has decided not to contest the presidential election.

"My fellow Democrats, I have decided not to accept the nomination and to focus all my energies on my duties as President for the remainder of my term. My very first decision as the party nominee in 2020 was to pick Kamala Harris as my Vice President. And it's been the best decision I've made," Biden said.

The 81-year-old president's decision comes four months before Americans go to the polls on November 5.

Such a decision from Biden comes amid a visible deterioration in his health. The president is currently in self-isolation at his Delaware residence after he tested positive with COVID-19.

Biden said he will speak to the nation later this week in more detail about his decision.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.