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

Butler, 44, was appointed by California Gov. Gavin Newsom on Sunday, two days after Feinstein, 90, died at her home in Washington. Butler is a longtime fundraiser and strategist in the state’s Democratic circles and was the head of Emily’s List, a national organization that raises money for women candidates who support abortion rights.

On the Senate floor Tuesday, Butler, 44, 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 Sen. Carol Moseley Braun of Illinois, who served one term in the 1990s.

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 said.

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.