The US Democratic Party has agreed to formally nominate Kamala Harris as its presidential candidate as soon as 1 August with a running mate being chosen by 7 August.
The plan was approved by the party's rules committee.
It means that both candidates would be in place before the Democrats convention in Chicago from 19-22 August.
Meanwhile, Ms Harris called on a rally of more than 6,000 black women to help her revitalise the party's presidential campaign, ahead of her Republican rival Donald Trump's return to the campaign trail.
She emerged as the Democrat candidate for the 5 November vote after President Joe Biden ended his re-election bid on Sunday in the face of intense opposition from fellow members who questioned his ability to win or to serve for another four years were he to do so.
Ms Harris, 59, the first black woman and Asian American to serve as vice president - who would also be a historic first as president if she prevails over Mr Trump - has shaken up a staid race and sparked new energy among Democrats.
Her surge will not go unanswered tomorrow, when Mr Trump, 78, holds his first rally since President Biden ended his campaign - in the battleground state of North Carolina.
The Trump campaign has insisted it is prepared for Ms Harris' candidacy, arguing she serves as a proxy for Mr Biden on the economic and immigration policies that contributed to the 81-year-old's sinking popularity with voters.
Ms Harris spoke at an event in Indianapolis, hosted by the Zeta Phi Beta Sorority, which was founded at Howard University, the historically black college that she attended.
She hopes to the multi-generational network of Black women - who played an important role in Mr Biden's 2020 victory - to deliver strong voter turnout for Democrats again in November.
"I thank you. And now, in this moment, our nation needs your leadership once again," Ms Harris said.
She and Mr Trump are closely competitive, according to opinion polls.
A Reuters/Ipsos poll published yesterday showed Ms Harris with a marginal 2% lead over Mr Trump - 44% to 42%.
A CNN poll conducted by SSRS showed the former president leading the vice president, 49% to 46%.
Both findings were within the polls' margins of error.
President Biden, who returned to Washington yesterday after isolating with Covid-19 at his home in Delaware, will address the United States from the White House tonight to explain his decision to exit the race.
He took the decision after a disastrous debate with Mr Trump last month raised questions about his ability to win the election, or to serve another four years if he succeeded.
Yesterday, Mr Trump took the unusual step of speaking to reporters on a conference call to underscore his campaign's line of attack on the border, saying Ms Harris was partially responsible for a record flow of migrants.
President Biden put her in charge of working with countries in central America to help stem the tide of migration, but she was not made responsible for border security.
"She's a radical left person, and this country doesn't want a radical left person to destroy it," Mr Trump said on the call. "She wants open borders. She wants things that nobody wants."
Ms Harris has not called for the removal of border controls.
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Mr Trump, coming off a triumphant week in which his party unified around his presidential bid after a failed assassination attempt two weekends ago, has had to watch as President Biden's sudden departure from the race shifted the narrative and sparked a surge of attention towards Ms Harris at his expense.
Her campaign chair Jen O'Malley Dillon said in a memo that Democrats would aim to compete in the swing states of Michigan, Wisconsin, Pennsylvania, North Carolina, Georgia, Arizona and Nevada, opening up a map that in the final weeks of Mr Biden's campaign had appeared to be more focused on the Midwest.
"This race is more fluid now - the vice president is well-known but less well-known than both Trump and President Biden, particularly among Dem-leaning constituencies," Ms O'Malley Dillon wrote.
The Harris campaign said it has raised $126 million (€116m) since Sunday, with 64% of donors making their first contribution of the 2024 campaign.
