Kamala Harris has made history as the first female, first black and first Asian-American US vice-president.
She was sworn in just before Joe Biden took the oath of office to become the 46th US president.
Ms Harris, who is of Indian-Jamaican heritage, initially ran for the Democratic nomination.
But Mr Biden won the race and chose Ms Harris as his running mate, describing her as "a fearless fighter for the little guy".
Prior to taking the oath at the US Capitol, Ms Harris paid tribute to the women who she says came before her.
"I stand on their shoulders," she said in a video.
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Eugene Goodman, the Capitol police officer who was hailed as a hero for steering a pro-Trump mob away from Senate chambers during the 6 January riot, escorted Ms Harris at the inauguration.
Who is Kamala Harris?
Ms Harris, 56, was 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".
After four years at Howard, Ms Harris went on to earn her law degree at the University of California, Hastings, and began her career in the Alameda County District Attorney's Office.
She became the district attorney - the top prosecutor - for San Francisco in 2003, before being elected the first female and the first African American to serve as California's attorney general, the top lawyer and law enforcement official in America's most populous state.
In her nearly two terms in office as attorney general, Ms Harris gained a reputation as one of the Democratic party's rising stars, using this momentum to propel her to election as California's junior US senator in 2017. She was only the second black woman ever elected to the US senate.
She launched her candidacy for president to a crowd of more than 20,000 in Oakland at the beginning of 2019.
But Ms Harris failed to articulate a clear rationale for her campaign, and gave muddled answers to questions in key policy areas like healthcare.
She was also unable to capitalise on the clear high point of her candidacy: debate performances that showed off her prosecutorial skills, often placing Mr Biden in the line of attack, most notably criticising his praise for the "civil" working relationship he had with former senators who favoured racial segregation.
She dropped out of the presidential race in December 2019.
But Mr Biden chose her as his number two in August, calling her "one of the country's finest public servants".
After Mr Biden was announced as the next president in November, Ms Harris tweeted a video of her congratulating her running mate.
"We did it, we did it Joe. You're going to be the next president of the United States!" she beamed.