After losing a race for governor in 1990, Feinstein was elected to the U.S. Senate in a 1992 special election. In November 1992, she became California's first female U.S. senator; shortly afterward, she became the state's senior senator when Alan Cranston retired in January 1993. Feinstein was reelected five times. In the 2012 election, she received 7.86 million votes, the most popular votes received by any U.S. Senate candidate in history.
Feinstein's last years in office were marred by poor health and concerns about her mental acuity to serve. In February 2023, Feinstein announced she would not seek reelection in 2024. She died in office in September 2023, at the age of 90. By the time of her death, Feinstein was the oldest sitting U.S. senator and member of Congress. She was also the longest-serving U.S. senator from California and the longest-tenured female senator in history.