California Gov. Gavin Newsom announced Sunday that he is appointing Laphonza Butler to the U.S. Senate to replace Sen. Dianne Feinstein, who died last week at the age of 90.

Butler posted on X, formerly Twitter, on Monday that she is "honored" to accept Newsom's appointment, and she said "I am ready to serve." Butler is currently the president of EMILYs List, a Democratic group dedicated to electing women who support abortion rights.

Vice President Kamala Harris plans to swear Butler in on Tuesday. 

In appointing Butler, Newsom is keeping a 2021 promise to appoint a Black woman to the role. Feinstein's seat is up for reelection in 2024, and three prominent House Democrats — Reps. Katie Porter, Adam Schiff and Barbara Lee — have already announced they are running. 

Butler will also serve as the crucial 51st vote for Senate Democrats, who have a slim majority in the upper chamber and are defending several seats in red states in 2024.

Butler will only be the third Black woman to serve in the Senate. Carol Moseley Braun of Illinois was the first, serving from 1993 to 1999. Harris was the second, from 2017 until becoming vice president in 2021. Butler was as a senior adviser on Harris' 2020 presidential campaign.

She is the second openly lesbian woman in the Senate, and the first Black lesbian woman in the Senate. She and her wife, Neneki, have a daughter named Nylah. Although Maryland voting records seen by CBS News show a Laphonza Butler of Silver Spring registered to vote in that state, Newsom's office said Monday that Butler will re-register in California, where she owns a home, when she is sworn in. 

What is Laphonza Butler's professional background?

According to her biography from EMILYs List, Butler grew up in Magnolia, Mississippi, and attended Jackson State University, a historically black university. 

In an interview with Elle in 2021, Butler said that her family wasn't the kind "that talked about elections or politics at the dinner table, but we were the family that talked about what it meant to be in service to others. What do we do to help somebody?"

In that same interview, she said that while she was working with the SEIU labor union, she was able to "connect it with the jobs my mom had."

"There have been parallels in my career and what I knew my mom experienced as a worker herself," Butler said. "I always felt like the work I've done has been my opportunity to continue my mom's journey and to make those jobs better for the children of those workers."

At the age of 30, Butler was elected the president of the biggest union in California, and the nation's largest homecare workers union, SEIU Local 2015. She also served as SEIU International's vice president and president of the SEIU California State Council.

Butler's biography says she spent 20 years in the labor movement, including working on the campaign to raise the minimum hourly wage to $15 in California, the first state in the country to do so. 

Butler was an adviser to Hillary Clinton's 2016 presidential campaign. 

In 2018, Butler and political consultants Ace Smith, Sean Clegg and Juan Rodriguez formed the political consulting firm SCRB Strategies. Rodriguez ran Harris' primary 2020 campaign, with Butler as senior adviser. 

After Harris left the race, Butler served as director of public policy and campaigns in North America for Airbnb.

What did Butler do with EMILYs List? 

Until being appointed to the Senate, Butler served as the president of EMILYs List, the group that supports women in office who support abortion rights. She was the first woman of color to hold that position. 

EMILYs List is fundraising juggernaut for Democrats, having raised nearly $68 million in the 2022 election cycle, according to OpenSecrets.

Butler told the news organization Capital B News in an interview in Feb. 2022 that after the 2016 election, "more than 60,000 women reached out to us from all over the country and wanted to offer themselves for public service."

"From a tactical point, we have created online communities for them to connect with each other, we have offered online training and made it accessible no matter what community that person is reaching out to us from, we have made sure that we are working to expand the state and local work of EMILYs List," she said.

EMILYs List issued a statement on Monday praising Butler as a "groundbreaking leader."

According to the statement from Newsom's office, Butler will step down from her role at EMILYs List when she joins the Senate.