The former first lady, who spent eight years in the White House with Mr Biden when he served as her husband’s vice president, is set to deliver the keynote speech on the first night of the convention.
Other speakers include Vermont senator Bernie Sanders, who ran Mr Biden close in the early stages of the Democratic primary, and whose supporters the former vice president is desperate to win over.
“I know Joe. He is a profoundly decent man guided by faith. He was a terrific vice president. He knows what it takes to rescue an economy, beat back a pandemic and lead our country,” Ms Obama says in the video released by the Democratic Party ahead of four nights of speeches.
“And he listens. He will tell the truth and trust science. He will make smart plans and manage a good team. And he will govern as someone who’s lived a life that the rest of us can recognise.”
The former first lady is one of a handful of speakers addressing the convention via video address who have a genuinely global appeal. Four years ago, at the Democrats’s convention, she urged Americans to make history by electing Hillary Clinton as their first woman president.
Also speaking to the convention on Monday, reduced to a succession of live streamed addresses because of the coronavirus pandemic, will be Mr Sanders.
Four years ago, he was the keynote speaker and delivered an address in which he urged his supporters to support Ms Clinton. He did so despite fury and acrimony after it emerged some officials in the Democratic Party had conspired against him and in favour of her.
Polling suggests that untold thousands of his supporters voted for Donald Trump in 2016, despite his appeal.
In his comments to be delivered four years later, the senator will again ask his supporters to vote for somebody they did not initially support.
“This election is the most important in the modern history of this country. In response to the unprecedented set of crises we face, we need an unprecedented response – a movement, like never before, of people who are prepared to stand up and fight for democracy and decency – and against greed, oligarchy and authoritarianism,” he will say, according to excerpts released beforehand.
“My friends, I say to you, and to everyone who supported other candidates in this primary and to those who may have voted for Donald Trump in the last election: the future of our democracy is at stake. The future of our economy is at stake.”
He will add: “The future of our planet is at stake. We must come together, defeat Donald Trump and elect Joe Biden and Kamala Harris as our next president and vice president. My friends, the price of failure is just too great to imagine.”
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