Gov. Gavin Newsom of California is expected on Monday to name Laphonza Butler, the president of Emily’s List and a former labor leader, to fill the vacancy left in the Senate by the death of Dianne Feinstein, several sources familiar with the decision confirmed on Sunday night.
Ms. Butler, 44, has been a fixture in California politics for nearly 15 years as a former leader of the state’s largest labor union and an adviser to Vice President Kamala Harris. In 2021, she became the first Black woman to take the helm at Emily’s List, the fund-raising powerhouse dedicated to the election of female candidates and supporters of reproductive rights.
The appointment would come four days after Senator Feinstein died at 90 on Thursday in Washington, D.C. The senator’s body was flown over the weekend back to San Francisco, where a memorial service has been scheduled for Thursday.
Ms. Butler, whose appointment was first reported by Politico, could not be immediately reached for comment.
In choosing Ms. Butler, Governor Newsom followed through on a pledge he made more than two years ago to name a Black woman to the Senate if a vacancy were to emerge.
But by the time of Ms. Feinstein’s death, three high-profile Democratic members of Congress had already entered the 2024 race to succeed her. Representatives Adam Schiff, Katie Porter and Barbara Lee have all been campaigning statewide in California for months.
Mr. Newsom, who is also a Democrat, told NBC News last month that he preferred not to influence next year’s primary election by giving one candidate an advantage. Instead, he said, he would pick an interim replacement.
His statement drew pushback from political allies of Ms. Lee, 77, who is Black and wants to serve in the office long term. But she is currently trailing the other two candidates in fund-raising and polling.
Over the weekend, as speculation gathered around the governor’s choice, members of the Congressional Black Caucus posted a letter to the governor, voicing “strong support for Congresswoman Barbara Lee for that appointment.” Advocacy organizations pushed for Ms. Lee as well.
“Barbara Lee, and Black women, are not mere caretakers, but the voting and organizing center of the national Democratic Party,” Aimee Allison, the founder of She the People, an organization that helps elect women of color in politics, said in a statement. The governor, she added, should use the full force of his political influence “to ensure Black women in California and every state are represented for the long term.”
While Governor Newsom last month viewed the appointment as an interim assignment and has said he would not want to interfere with the primary, his chief spokesman, Anthony York, indicated on Sunday that the governor would not demand that his appointee stay out of the 2024 Senate race.
In a post on X, the social media site formerly known as Twitter, Mr. York agreed with Representative Cori Bush, Democrat of Missouri, who said “there shouldn’t be any strings attached” to the appointment.
That leaves open the possibility that Ms. Butler — a prolific fund-raiser at Emily’s List — could still enter the primary for the permanent Senate seat.
Ms. Butler would become the first openly L.G.B.T.Q. senator to represent California. Scott Wiener, a Democratic state senator, celebrated the appointment on Sunday night.
“L.G.B.T.Q. people are being viciously attacked in the United States right now, and elevating a Black lesbian to the U.S. Senate is a powerful statement,” said Mr. Wiener, a gay leader from San Francisco who has championed legislation protecting L.G.B.T.Q. rights.
This is a developing story. Check back for updates.
Shane Goldmacher, Heather Knight and Reid J. Epstein contributed reporting.