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 will face President Donald Trump in the election on 3 November.
Vice-President Mike Pence remains the Republican incumbent’s running mate.
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.