Senator Kamala Harris of California is interviewed after the second night of the first Democratic primary debate in Miami, Florida, the United States, on June 27, 2019. Photo: Xinhua

Former US Vice President and presumptive Democratic nominee Joe Biden announced on Tuesday that he has picked Senator Kamala Harris of California as his running mate.

In a tweet, Biden called Harris "a fearless fighter for the little guy, and one of the country's finest public servants."

Elected in 2016, Harris, now 55, was the second African American woman in history elected to the US Senate. Before that, she served as attorney general of California.

With Biden's selection, she becomes the third woman in US history to serve as a vice presidential candidate, following Geraldine Ferraro as the Democratic vice presidential pick in 1984 and Sarah Palin as the Republican vice presidential pick in 2008.

"Back when Kamala was Attorney General, she worked closely with Beau," Biden continued in his tweet, referring to his late son who was then the attorney general of Delaware and who died in 2015 from brain cancer. "I watched as they took on the big banks, lifted up working people, and protected women and kids from abuse. I was proud then, and I'm proud now to have her as my partner in this campaign."

In a tweet following Biden's announcement, Harris hailed the presumptive Democratic nominee as someone who "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," she added.

Biden and Harris will appear together and speak in Biden's hometown of Wilmington, Delaware, on Wednesday, according to the Biden campaign.

The daughter of Indian and Jamaican immigrants, Harris announced her bid for the White House in January 2019. Due to a shortage of funds, she dropped out of the race less than a year later.

In March 2020, Harris, who famously called out Biden over racial issues in a Democratic primary debate, endorsed him. Having spent most of her political career as a prosecutor, the senator rose to national prominence as a leader on both racial equality issues and criminal justice reform.

"She's been a leader on criminal justice and marriage equality. And she has focused like a laser on the racial disparities as a result of the coronavirus," Biden said Tuesday of Harris, who, like himself, is considered a moderate Democrat.

Harris winning the bid for vice presidential candidacy capped a long process of which the result was previously expected in the first week of August.

Biden, who has promised to name a female running mate, postponed the announcement as the contest became increasingly more fluid than observers had thought, with Suzan Rice, former national security adviser in the administration of former president Barack Obama, and Michigan Governor Gretchen Whitmer seemingly gaining momentum in the final days leading up to the announcement.

Those who vied for the post with Harris quickly reacted to Biden's decision and supported his pick.

Rice said Harris "is a tenacious and trailblazing leader." Whitmer said she was "extraordinarily proud to support" Harris and Biden. Elizabeth Warren, once a Democratic presidential candidate on the progressive camp who endorsed Biden after dropping out, tweeted that Harris "will be a great partner to @JoeBiden in making our government a powerful force for good in the fight for social, racial, and economic justice."

Other prominent Democrats also voiced their support for Harris. House Speaker Nancy Pelosi said the senator "will continue her legacy of trailblazing leadership to move our nation forward." Obama said Harris "is more than prepared for the job." Former President Bill Clinton said she and Biden "make a strong team." Hillary Clinton, the 2016 Democratic presidential nominee, called on supporters to join her in getting Harris elected.

In his first public comment during a news briefing at the White House on Tuesday afternoon, President Donald Trump said Harris was "my number one draft pick, and we'll see how she works out."

He said Harris "was extraordinarily nasty to Judge (Brett) Kavanaugh" -- the Trump-appointed Supreme Court justice who was alleged of sexual misconduct -- during Senate hearings, adding that "she did very poorly in the primaries and now she's chosen so let's see how that all works out."

Hours earlier, Trump campaign senior adviser Katrina Pierson in a statement accused Harris of attempting to "bury her record as a prosecutor, in order to appease the anti-police extremists," meanwhile claiming that the selection of Harris "is proof that Joe Biden is an empty shell being filled with the extreme agenda of the radicals on the left."