Democratic presidential candidate Joe Biden has named Senator Kamala Harris as his running mate – the first black woman and Asian American in the role.
Once a rival for the top job, the California senator of Indian-Jamaican heritage had long been considered the front-runner for the number two slot.
The former California attorney general has been urging police reform amid nationwide anti-racism protests.
Mr Biden will face President Donald Trump in the election on 3 November.
At a White House news conference on Tuesday, Mr Trump, a Republican, described Ms Harris as “my number one draft pick”.
Ms Harris will debate Mr Trump’s running mate, Vice-President Mike Pence, on 7 October in Salt Lake City, Utah.
Only two other women have been nominated as vice-presidential candidates – Sarah Palin by the Republican party in 2008 and Geraldine Ferraro by the Democrats in 1984. Neither made it to the White House.
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.
What did Biden and Harris say?
Mr Biden tweeted that he had “the great honour” to name Ms Harris as his number two.
Profile: Who is Kamala Harris?
He described her as “a fearless fighter for the little guy, and one of the country’s finest public servants”.
He noted how she had worked closely with his late son, Beau, when she was California’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 I’m proud now to have her as my partner in this campaign.”
Ms Harris later tweeted that Mr Biden “can unify the American people because he’s spent his life fighting for us. And as president, he’ll build an America that lives up to our ideals.
“I’m honored to join him as our party’s nominee for Vice President, and do what it takes to make him our Commander-in-Chief.”
The campaign announced that Mr Biden and Ms Harris will deliver remarks in Wilmington, Delaware, on Wednesday afternoon on “working together to restore the soul of the nation and fight for working families to move the country forward”.
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 was convulsed by social unrest over police brutality against African Americans, a key voting bloc to the Democratic Party.