Democratic presidential candidate Joe Biden and Kamala Harris will make their first joint appearance as running mates in Delaware later on Wednesday.
Mr Biden, who will face President Donald Trump in the election on 3 November, named Kamala Harris as his vice-presidential pick on Tuesday.
He is expected to formally introduce Ms Harris as his choice for vice-president and both are expected to speak.
Senator Harris is the first black woman and South Asian American in the role.
Mr Biden and Ms Harris will deliver remarks in Wilmington, Delaware, later on Wednesday on “working together to restore the soul of the nation and fight for working families to move the country forward”, the Biden campaign said.
Who is Kamala Harris?
Ms Harris, 55, was born in Oakland, California, to two immigrant parents - an Indian-born mother and Jamaican-born father.
She went on to attend Howard University, one of the nationâ€™s preeminent historically black colleges and universities. She has described her time there as among the most formative experiences of her life.
Ms Harris says she has always been comfortable with her identity and simply describes herself as “an American”.
In 2019, she told the Washington Post that politicians should not have to fit into compartments because of their colour or background. “My point was: I am who I am. Iâ€™m good with it. You might need to figure it out, but Iâ€™m fine with it,” she said.
How did she become Bidenâ€™s running mate?
Ms Harris ran for the Democratic nomination for presidential candidate but dropped out in December after failing to make headway.
She had long been considered the front-runner for the number two slot even though she repeatedly clashed with Mr Biden during the primary election debates. In one of their clashes, she criticised Mr Bidenâ€™s praise for the “civil” working relationship he had with former senators who favoured racial segregation.
Mr Biden pledged in March to name a woman on the ticket. He had faced mounting calls to pick a black woman in recent months as the nation has been convulsed by social unrest over police brutality against African Americans, a key voting bloc for the Democratic Party.
A woman of colour has never been appointed to a presidential ticket by either of the two main American political parties. No woman has won the US presidency either.
On Tuesday, Mr Biden announced by text message and in an email to his followers that he had chosen the 55-year-old senator as his number two. He described her as “a fearless fighter for the little guy, and one of the countryâ€™s finest public servants”.
He also noted how she had worked closely with his late son, Beau, when she was Californiaâ€™s attorney general. “I watched as they took on the big banks, lifted up working people, and protected women and kids from abuse,” he tweeted.
“I was proud then, and Iâ€™m proud now to have her as my partner in thisÂ campaign.” Ms Harris said she was “honoured to join him as our partyâ€™s nominee for Vice President”.
What has the reaction been?
President Donald Trump quickly attacked Ms Harris after Mr Biden made his announcement. The president told reporters: “Sheâ€™s a person thatâ€™s told many, many stories that werenâ€™t true.”
He also said that he thought Ms Harris was “one of the meanest, most horrible” people in the US Senate and praised his pick for vice-president, Mike Pence.
Ms Harris will take part in a debate with Mr Trumpâ€™s running mate, Vice-President Mike Pence, on 7 October in Salt Lake City, Utah.
In last yearâ€™s race to be the Democratic nominee, Kamala Harris showed herself to be a forceful speaker, launching blistering attacks on Donald Trump.
Hillary Clinton, who lost to Mr Trump in the 2016 election, said she was “thrilled to welcome [Ms Harris] to a historic Democratic ticket”. “Sheâ€™s already proven herself to be an incredible public servant and leader,” she added.
Former US President Barack Obama - whom Mr Biden served as vice-president for eight years - tweeted: “She is more than prepared for the job. Sheâ€™s spent her career defending our Constitution and fighting for folks who need a fair shake.
“This is a good day for our country. Now letâ€™s go win this thing.”
What does a running mate do?
The role of a vice-presidential running mate is not always clearly defined.
One of the traditional roles is to go on the offensive in exposing the oppositionâ€™s weaknesses, while the presidential nominee focuses on communicating the partyâ€™s message, says the BBCâ€™s North America reporter Anthony Zurcher.
Constitutionally, the vice-president steps in to the top job should the president die or leave office during his or her term.
Mr Biden will turn 78 in November, meaning should he be elected he will be the oldest US president in history (Ronald Reagan was 77 when he left office).
His age means Mr Bidenâ€™s vice-presidential choice may come under extra scrutiny.
Only two other women have been nominated as vice-presidential candidates for a major party - Sarah Palin by the Republican party in 2008 and Geraldine Ferraro by the Democrats in 1984. Neither were on the winning ticket.
Women VP candidates
- Geraldine Ferraro was the first woman who ever ran for vice-president on a major-party ticket
- Time magazineâ€™s cover story at the time featured a photo of Ms Ferraro with the headline “A Historic Choice”
- But much of the subsequent coverage was sexist with Ms Ferraro attacked for being a working mother
- Sarah Palin is the only woman to have run for vice-president on a Republican ticket
- The Alaska governor also complained about the mediaâ€™s coverage of her, in particular a Newsweek cover that used a photo of her in running gear
Sarah Palin congratulated Ms Harris on being the third woman to become a running mate for a major party and also offered plenty of advice on her Instagram account, including “trust no-one new” and “donâ€™t get muzzled - connect with the media and voters in your own unique way”.