WILMINGTON, Del. (News Nation) — Democratic U.S. presidential candidate Joe Biden announced California Sen. Kamala Harris as his running mate on Tuesday, making history by selecting the first Black woman on a major party’s presidential ticket.

The 55-year-old Harris was elected to the Senate in 2016 after serving as California’s attorney general. Harris competed against Biden for the Democratic presidential nomination but left the race before voting began as she struggled to raise money. Harris became a top contender for the No. 2 spot after her own White House campaign ended.

In adding Harris to the ticket, Biden can point to her relatively centrist record on issues such as health care and her background in law enforcement in the nation’s largest state.

Biden, who spent eight years as President Barack Obama’s vice president, has spent months weighing who would fill that same role in his White House. He pledged in March to select a woman as his vice president.

Biden took to Twitter for the official announcement.

“I have the great honor to announce that I’ve picked @KamalaHarris — a fearless fighter for the little guy, and one of the country’s finest public servants — as my running mate.”

Leading contenders for the vice presidential nod included Massachusetts Sen. Elizabeth Warren, a leading progressive, Florida Rep. Val Demings, whose impeachment prosecution of Trump won plaudits, California Rep. Karen Bass, who leads the Congressional Black Caucus, former Obama national security adviser Susan Rice and Atlanta Mayor Keisha Lance Bottoms, whose response to unrest in her city garnered national attention.

A woman has never served as president or vice president in the United States. Two women have been nominated as running mates on major party tickets: Democrat Geraldine Ferraro in 1984 and Republican Sarah Palin in 2008. Their party lost in the general election.

Shortly after the being named Biden’s running mate, Harris responded with a tweet.

“.@JoeBiden 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.”

Born in Oakland to a Jamaican father and Indian mother, Harris won her first election in 2003 when she became San Francisco’s district attorney. In the role, she created a reentry program for low-level drug offenders and cracked down on student truancy.

She was elected California’s attorney general in 2010, the first woman and Black person to hold the job, and focused on issues including the foreclosure crisis. She declined to defend the state’s Proposition 8, which banned same-sex marriage and was later overturned by the U.S. Supreme Court.

As her national profile grew, Harris built a reputation around her work as a prosecutor. After being elected to the Senate in 2016, she quickly gained attention for her assertive questioning of Trump administration officials during congressional hearings. In one memorable moment last year, Harris tripped up Attorney General William Barr when she repeatedly pressed him on whether Trump or other White House officials pressured him to investigate certain people.

Harris has taken a tougher stand on policing since George Floyd’s killing. She co-sponsored legislation in June that would ban police from using chokeholds and no-knock warrants, set a national use-of-force standard and create a national police misconduct registry, among other things. It would also reform the qualified immunity system that shields officers from liability.

The list included practices Harris did not vocally fight to reform while leading California’s Department of Justice. Although she required DOJ officers to wear body cameras, she did not support legislation mandating it statewide. And while she now wants independent investigations of police shootings, she didn’t support a 2015 California bill that would have required her office to take on such cases.

“We made progress, but clearly we are not at the place yet as a country where we need to be and California is no exception,” she told The Associated Press recently. But the national focus on racial injustice now shows “there’s no reason that we have to continue to wait.”

Former President Barack Obama released a statement supporting his former vice president’s running mate choice, saying, “Joe Biden nailed this decision.”

Biden and Harris will appear together in Delaware on Wednesday.