As she weighed whether to enter the race, Harris spoke about the challenges of running a campaign that would attempt to break several barriers.
If elected, she would be the first woman, the first woman of Asian heritage and the first African-American woman as president.
"Let's be honest. It's going to be ugly," Harris told MSNBC's Mika Brzezinski during a December conference in San Francisco. "When you break things, it is painful. And you get cut. And you bleed."
Her announcement came on a day when the US celebrates the legacy of civil rights leader Martin Luther King. Her campaign noted that Shirley Chisholm, the first black woman to run for president in a major party, launched her campaign 47 years ago this week.
Harris also plans to travel to Columbia, South Carolina, on Saturday to speak at the Pink Ice Gala, an event held by the local Gamma Nu Omega chapter of Alpha Kappa Alpha, the group Harris joined while at Howard University. South Carolina will hold the first primary in 2020 dominated by African-American voters.
In her announcement, Harris drew on history, saying it was "very important" to her to tie her campaign to Martin Luther King and the civil rights movement. She said he had a realistic idea of America's flaws, but remained "aspirational".
She said: "We know that we've not yet reached those ideals. Our strength is that we fight to reach those ideals."
Harris is relatively unknown nationally - a CNN survey in September found that 51 per cent of registered voters had never heard of her - and has recently tried to introduce herself through the requisite campaign book The Truths We Hold, which was released on January 8.
In the Senate she has earned a reputation for sharp questioning and a sceptical approach to Trump Administration officials. From her seat on the Senate Judiciary Committee she has been one of the body's more pointed interrogators, particularly during high-profile moments such as the confirmation hearings for Supreme Court Justice Brett Kavanaugh.
During a tense exchange with then-Attorney General Jeff Sessions over Trump campaign contacts with Russia, Sessions stopped her.
"I'm not able to be rushed this fast," he said. "It makes me nervous."
Harris' rich mixture of heritage has led some supporters to refer to her as "the female Barack Obama". The former Democratic president also launched his presidential campaign two years after joining the Senate.
As a child, Harris attended a Hindu temple and a black Baptist church. Her name Kamala (which she pronounces "comma-la" or "calm-ala") comes from the Sanskrit word for lotus plant.
Harris' late mother immigrated to the United States from India as an adult and became a physician specialising in breast cancer. Her father became an economics professor at Stanford University. They divorced when Harris was young, and her mother raised her and her younger sister, Maya.
Harris attended Howard University in Washington and the University of California Hastings College of the Law. She then set out on a career as a prosecutor.
Her motto, she told the San Francisco Chronicle in 2009, is a saying her mother had - "you may be the first, but make sure you're not the last" - and her political career has been marked by firsts.
When she ran in 2003 and unseated her onetime boss, San Francisco District Attorney Terence Hallinan, she became the first black woman to be elected district attorney in California. When she was elected attorney general of California in 2010, she became the state's first female, the first African-American and first Asian-American to hold the position.
Her tenure as attorney general was marked by efforts to protect consumers and fight sexual trafficking. But she also came under fire for tough stances against felons whose guilt fell under question.
Some of that tenure is bound to come under scrutiny during her presidential campaign, but she nonetheless is expected to highlight her career as a prosecutor. The campaign slogan in her announcement video is "For the People," which campaign advisers said was a nod to her rising in court to say, "Kamala Harris, for the people."
In her first remarks after announcing her presidential campaign, Harris described the criminal justice system as "horribly flawed" and in need of change. Yet, she said, all communities also support law enforcement.
"There is a lot of work to do, but to suggest it's one or the other, I don't buy that," she said.
In 2014, she married Doug Emhoff, a media, entertainment and intellectual property partner with two children from his earlier marriage.
Harris' Senate colleagues Elizabeth Warren and Kirsten Gillibrand have announced presidential bids. Among those expected to join the race are senators Cory Booker, Sherrod Brown and Amy Klobuchar. Also pondering a run is Bernie Sanders.
In the weeks before the November elections, Harris made trips to Iowa and South Carolina, both early-voting states. She is also positioned to do well in her home state, which has moved its primary from June to March of 2020, as well as neighbouring Nevada.
Harris has faced controversy: One of her senior advisers, Larry Wallace, resigned in December amid questions about a US$400,000 lawsuit that was settled in 2017. The suit resulted from allegations that he sexually harassed a female assistant when they worked for Harris at the California Department of Justice.
Among several allegations in a lawsuit cited by the Sacramento Bee, Wallace placed a printer underneath his desk and forced his female assistant to replace ink or paper in it every day, even when she asked to move it to another location to avoid crawling under his desk in dresses or skirts.
Harris has played a prominent role as Washington confronted the #MeToo movement, and was among the first senators to call on Senator Al Franken to resign last year amid allegations of misconduct.
Harris is planning to base her presidential campaign in Baltimore, with a second office in Oakland. It will be led by Juan Rodriguez, who was the campaign manager of her 2016 Senate campaign and was also a senior adviser to California Governor Gavin Newsom's campaign.
The campaign chair will be Maya Harris, the candidate's sister and a former senior adviser to Hillary Clinton's presidential campaign.
Other members of her campaign team include prominent Democratic lawyer Marc Elias as general counsel, Angelique Cannon as national finance director; David Huynh as senior adviser; and Lily Adams as communications director.
