WASHINGTON (AP) — Former union leader and Democratic insider Laphonza Butler was sworn in as the newest member of the Senate on Tuesday, replacing California Senator Dianne Feinstein after her death and becoming only the third black female senator in history.

Butler was appointed by California Governor Gavin Newsom on Sunday, just two days after Feinstein died at her home in Washington. Butler is a long time fundraiser and strategist in the state’s Democratic circles and was the head of Emily’s List, a national organisation that raises money for women candidates who support abortion rights.

The new senator was sworn in by Vice President Kamala Harris, who served as the second Black female senator until she resigned in 2021 to join President Joe Biden in the White House. The first was Democratic Senator Carol Moseley Braun of Illinois, who served one term in the 1990s.

With dozens of supporters and family members looking down from the gallery, Butler smiled broadly as she walked down the centre aisle of the Senate alongside Democratic Senator Alex Padilla of California and Senate Majority Leader Chuck Schumer. After Harris administered the oath of office, members of the Senate from both parties crowded around her to shake her hand.

Schumer, D-NY, said that “today, the Senate takes another step towards fully reflecting our vibrant democracy.”

He said Butler has “dedicated her entire career to fighting for others – fighting for women, fighting for working families and fighting for the cause of justice.”

After she was sworn in, Biden called her to congratulate her, the White House said.

The Congressional Black Caucus also held a ceremonial swearing-in for Butler. “Her background and years of experience will bring a much-needed perspective to the Senate, which currently does not have any Black women,” CBC Chairman Steven Horsford, D-Nevada, said in a statement after she was appointed.

Butler is also the first openly LGBTQ+ senator from California.

Though she has never held elective office, Newsom praised her “deep knowledge” of the legislative process and said she was the kind of candidate he would build “if I had to literally design from my imagination.”

“She’s the only choice,” Newsom added.

Butler is well known inside California’s Democratic party apparatus. Her credentials include working for nearly two years with a consulting firm tied closely to Newsom and founded by his top political lieutenants. She also served as a senior adviser to Harris’ 2020 presidential campaign.

It is unclear if Butler will run to hold the seat when Feinstein’s term ends next year. A competitive race for Feinstein’s seat is already underway among three prominent House Democrats, Reps. Katie Porter, Adam Schiff and Barbara Lee, who is Black. The governor has said he didn’t want to tip the scales in the 2024 race by choosing among those candidates.

Newsom said he told Butler to “do what you think is best for you and the state of California, and you make that judgment completely independent of any expectations from me.”

Butler, 44, comes from a working-class family. Her father, a small-business owner, died from a terminal illness when she was 16. Her mother worked as a classroom aide, a home care provider, a security guard and a bookkeeper while caring for Butler and her two siblings, the governor’s office said. She was elected president of the state’s largest labour union in the early 2010s, back when the nation was reeling from the Great Recession.

Butler has also worked for corporate clients, including Airbnb and Uber.