Originally Published: 01 OCT 23 23:26 ET

Updated: 02 OCT 23 13:13 ET

By Kyung Lah and Kaanita Iyer, CNN

(CNN) — California Gov. Gavin Newsom will appoint Laphonza Butler, the president of EMILY’s List, to fill the late Democratic Sen. Dianne Feinstein’s Senate seat, his office confirmed Sunday evening.

Butler will become the first out Black lesbian to join Congress, according to Newsom. She will also be the sole Black female senator serving in Congress and only the third in US history. Feinstein, the longest-serving female US senator in history, died last week at 90.

“I am honored to accept Gov. Newsom’s nomination to be a U.S. Senator for a state I have long called home,” Butler said in a statement Monday, adding that she is “humbled by the Governor’s trust.”

“For women and girls, for workers and unions, for struggling parents waiting for our leaders to bring opportunity back to their homes, for all of California, I’m ready to serve,” she said.

The selection of Butler, first reported by Politico, comes as Democrats hold a narrow Senate majority and uncertainty looms over New Jersey Sen. Bob Menendez’s political future amid outcry from his Democratic colleagues over his federal indictment.

Butler has been the president of EMILY’s List, which works to elect Democratic women who support abortion rights, since the group’s board of directors appointed her in 2021, when she became the first woman of color to lead the organization. She previously worked at Airbnb as a director of public policy and campaigns and has a long history working in California politics, including as an adviser to Vice President Kamala Harris’ 2020 presidential campaign. But much of her background is in the labor movement, serving as a union president in California.

Several high-profile Democratic candidates launched campaigns earlier this year to succeed Feinstein, who announced in February that she would not run for reelection. They include a trio of House Democrats: Reps. Adam Schiff, a former House Intelligence chairman who is backed by former House Speaker Nancy Pelosi; Katie Porter, a former deputy chair of the Congressional Progressive Caucus; and Barbara Lee, a former chair of the Congressional Black Caucus and a member of House Democratic leadership. Also in the race are Democrat Lexi Reese, a tech executive, and Republican lawyer Eric Early, who ran unsuccessfully for state attorney general in 2022.

Newsom previously pledged to appoint a Black woman to Feinstein’s seat should the senator resign before her term’s end. Many had urged Newsom to appoint Lee, a longtime representative from Oakland and the only Black woman running for the seat, including the Congressional Black Caucus, which sent a letter to Newsom asking him to choose Lee just hours before his announcement.

But the governor said last month that he would not appoint any of the candidates currently seeking the office, though Newsom’s office said Monday that there were no conditions placed on Butler and that any decision to run for a full term would be her own.

Butler moved to Maryland in 2021 around the time she was chosen to lead EMILY’s List, public records show. She was registered to vote in Maryland in 2022, according to public records, but Newsom’s office said Monday, in response to questions about Butler’s residency, that she has re-registered to vote in California.

“As we mourn the enormous loss of Sen. Feinstein, the very freedoms she fought for – reproductive freedom, equal protection, and safety from gun violence – have never been under greater assault. Laphonza has spent her entire career fighting for women and girls and has been a fierce advocate for working people,” Newsom said in a statement on X.

This is Newsom’s second Senate appointment. After the 2020 election, the governor appointed Alex Padilla, then California’s secretary of state, to succeed Kamala Harris following her election to the vice presidency. Padilla became the first Latino senator from California, but Newsom was criticized for not choosing a Black woman, leaving the chamber without a Black female senator. He later appointed Shirley Weber, a Black woman, to succeed Padilla as secretary of state.

Padilla said in a statement he was “honored to welcome” Butler to the Senate and said she “has been a strong voice for working families, LGBTQ rights, and a champion for increasing women’s representation in politics.”

California will hold two Senate elections next November: a special election for the remaining months of Feinstein’s term until January 2025 and another for a full six-year term.

Lee, who is running for Feinstein’s seat in next year’s election, said she is “singularly focused on winning my campaign for Senate,” in a post on X.

Primaries for both races will be held in March, and, under the California system, all candidates will run on the same ballot, with the top two, regardless of party, advancing to the general election.

California also held two Senate elections for the same seat in 2022, following Padilla’s appointment. He won both races by similar margins.

This story has been updated with additional information.