ANAHEIM, Calif. — California Gov. Gavin Newsom plans to appoint Emily’s List president Laphonza Butler to fill the seat held by the late Sen. Dianne Feinstein, who died last week at age 90, according to two people with knowledge of the decision, who spoke on the condition of anonymity to share information not yet public.

The interim appointment will extend until at least November 2024. Feinstein had planned to step down at the end of her term, in January 2025. Three of California’s top Democrats — Reps. Barbara Lee, Katie Porter and Adam B. Schiff — are in a contentious three-way primary contest for that seat, in what is likely to be the most expensive congressional contest in the nation next year. The appointment helps Democrats hold onto their narrow margin of control of the Senate.

With the appointment, Newsom, a Democrat who is widely viewed as a future White House contender, fulfilled the promise that he made in 2021 to appoint a Black woman to the chamber.

He made that vow shortly after appointing Alex Padilla to fill the seat of Kamala D. Harris as she headed to the White House to serve as Joe Biden’s vice president. Padilla became the first Latino senator to represent California, but Harris’s departure meant there were no longer any Black women serving in the U.S. Senate. Butler will be the only Black woman currently serving in the Senate.