She was born on June 22, 1933, in San Francisco. Her father was Leon Goldman, a surgeon; and her mother, Betty, had been a model. Young Dianne attended a Jewish day school and then a Catholic school before enrolling in Convent of the Sacred Heart High School, from which she graduated in 1951. Four years later, she earned a Bachelor of Arts degree in history from Stanford University.

She began her career of service on the California Women's Parole Board and was a member from 1960 to 1966. She won election to the San Francisco Board of Supervisors three years later and served on that body until 1978. In her last year, she won election as board president.

Feinstein definitely wanted to be mayor of the city. She ran twice, in 1971 and in 1975, and lost both times. She finally became mayor on Nov. 27, 1978, as the result of an assassination. Then-Mayor George Moscone and another supervisor, Harvey Milk, were shot dead by former supervisor Dan White; and Feinstein, as acting Board of Supervisors president, became acting mayor. Her fellow supervisors voted to appoint her mayor and on Dec. 4, 1978, she became the city's first female chief executive. She remained in the position for 10 years, having survived a recall attempt because of her support for a handgun ban.

In 1990, Feinstein ran for Governor of California, representing the Democratic Party. The winner of that election was Republican Pete Wilson, who resigned his seat in the U.S. Senate in order to serve as governor. Feinstein ran to claim his vacant Senate seat in 1992 and won that election, significantly defeating Republican John Seymour.

Wilson's term expired in 1994, and Feinstein ran again, winning re-election, a feat she achieved again in 2000, 2006, 2012, and 2018. She had already announced that she would not seek re-election in 2024.

She claimed many firsts in her long tenure in the Senate:

• First woman to chair the Judiciary Committee
• First woman to chair the Rules Committee
• First woman to chair the Select Committee on Intelligence.

Long a proponent of gun laws, she championed the passage of a federal assault weapons ban in 1994. That law had a 20-year life, and she unsuccessfully campaigned for a replacement law several times thereafter.

Another of her targets was the Central Intelligence Agency, whom she supported in principle but insisted on accountability in exchange. One of her many projects in that area was an exhaustive look into interrogation techniques employed by intelligence and military personnel in the days and years following the attacks on New York City and Washiington, D.C., on September 11, 2001.

She was known as a centrist lawmaker in an era of increasing polarization. She sided with conservatives at times, angering her own party; a great many times she voted more liberally minded.

She was the longest-serving woman in the U.S. Senate and the longest-serving Senator from her home state of California.

Feinstein had married three times:

• In 1956, she married Jack Berman, who was working in the office of the San Francisco District Attorney; they had a child, Katherine, in 1957, but divorced two years later.
• She married neurosurgeon Bertram Feinstein in 1962; he died in 1978.
• Her last husband was Richard Blum, an investment banker. They married in 1980, and he died in 2022.

She suffered from health problems in her last year, including a case of shingles that required hospitalization and encephalitis that led to partial paralysis. Consequent balance problems led to a fall at her home, which also required hospitalization.