Biden took centre stage on opening night of the Democratic National Convention, drawing an extended standing ovation from the party faithful, who have swiftly moved on without him.
Wiping away tears after being introduced by his daughter Ashley and waving to the crowd that held signs saying, "We (heart) Biden," a smiling Biden said: "I love you."
"Are you ready to vote for freedom? Are you ready to vote for democracy and for America? Let me ask you, are you ready to elect Kamala Harris and Tim Walz?" Biden said.
Joe Biden wipes his eyes after embracing his daughter Ashley Biden. (AP PHOTO)
Biden's address in Chicago kicked off a four-day event fuelled by enthusiasm for Harris and relief that Biden abandoned his own re-election bid and endorsed her to replace him.
The president's reluctant decision to step aside on July 21 came after heavy pressure from party leaders who worried the 81-year-old incumbent was too old to win or serve another four years.
In his speech, Biden touted his administration's accomplishments - boosting the US economy and strengthening US alliances abroad - and made the case for Americans to elect Harris as his White House successor.
He condemned the racism and white supremacy that continue to plague America, saying they had no place in the nation.
Earlier in the evening, Harris has made a surprise appearance drawing cheers from the crowd as she vowed to defeat Republican rival Donald Trump in the US election.
"Let us fight for the ideals we hold dear and let us always remember, when we fight we win!" Harris, the US vice president, said in brief remarks that drew roars from the crowd.
Harris, 59, will formally accept the nomination on Thursday.
Delegates cheer Joe Biden during the first day of Democratic National Convention. (AP PHOTO)
Harris is riding a historic whirlwind into the convention: her campaign has broken records for fundraising, packed arenas with supporters, and turned opinion polls in some battleground states in Democrats' favour.
Earlier she proposed to increase the corporate tax rate to 28 per cent from 21 per cent if she wins the November election.
Harris campaign spokesman James Singer said the move would be part of "a fiscally responsible way to put money back in the pockets of working people and ensure billionaires and big corporations pay their fair share".
When Trump was president, he slashed the corporate tax rate to 21 per cent from 35 per cent and implemented other tax breaks that are set to expire next year.
Trump has vowed to make the cuts permanent. Changes to the US tax code require approval by Congress.
Trump pledged on Monday to rescind a Biden administration rule limiting power plant pollution and reiterated a promise to block Nippon Steel's planned purchase of US Steel.
"I will stop Japan from buying United States Steel," Trump said. "They shouldn't be allowed to buy it."
Donald Trump pledged to eliminate rules which limit air and water pollution from power plants. (EPA PHOTO)
In the most detailed economic remarks he has offered on the campaign trail so far, Trump also ratcheted up his pledge to radically limit foreign access to domestic markets, saying he would ensure the supply chain for essential goods would be 100 per cent American if he wins the November 5 election.
He did not elaborate on how he would accomplish that goal beyond advocating broad measures, like imposing tariffs on other nations.
US Steel said in a statement after Trump's remarks that it is "committed to the transaction with Nippon Steel, which is the best deal for our employees, shareholders, communities, and customers."
The former US president spoke to a crowd of supporters on a factory floor in the working-class city of York, Pennsylvania.
Biden in March said it is vital for US Steel "to remain an American steel company that is domestically owned and operated".
Trump also pledged to eliminate rules published by the Environmental Protection Agency in April, which limit air and water pollution from power plants and are designed to cut over one billion metric tonnes of greenhouse gas emissions by 2047. The electricity sector is responsible for nearly a quarter of US greenhouse gas pollution, according to the EPA.
"It's a disaster for our country," Trump said. "Instead of shutting down power plants, we will open dozens and dozens more, and they'll happen fast."
