Democratic presidential candidate, Joe Biden, has named Senator Kamala Harris as his running mate. She is the first black woman to serve 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 position.
The former California attorney-general has been urging police reform amid anti-racism protests.
Mr Biden tweeted that he had “the great honour” to name Ms Harris as his number two.
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.”
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 will face President Donald Trump in the election on 3 November.
Vice-President Mike Pence remains the Republican incumbent’s running mate.
The Trump campaign said the choice of running mate was proof that Mr Biden is “an empty shell being filled with the extreme agenda of the radicals on the left”.
“Not long ago, Kamala Harris called Joe Biden a racist and asked for an apology she never received,” the campaign said.
“Clearly, Phony Kamala will abandon her own morals, as well as try to bury her record as a prosecutor, in order to appease the anti-police extremists controlling the Democrat Party.
“In her failed attempt at running for president, Kamala Harris gleefully embraced the left’s radical manifesto, calling for trillions of dollars in new taxes and backing Bernie Sanders’ government takeover of healthcare.”
Harris 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 nation’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’s always been comfortable with her identity and simply describes herself as “an American”.
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.