Dan White was born on September 2, 1946, in Long Beach, California. He was the second of nine children in his family, which was of working-class Irish-American background. When he was young, his family moved to the Visitacion Valley neighborhood of San Francisco. Dan attended Archbishop Riordan High School but was expelled for violent behavior during his junior year. After his expulsion, he switched to Woodrow Wilson High School, which is now known as Phillip and Sala Burton High School.

In June 1965, Dan White joined the United States Army. He served as a sergeant in the 101st Airborne Division during the Vietnam War, from 1969 to 1970. He was honorably discharged in 1971. After his time in the army, he worked as a security guard at A. J. Dimond High School in Anchorage, Alaska. White then returned to San Francisco and became a police officer with the San Francisco Police Department. He left the police force after claiming he reported another officer for mistreating a suspect. Following this, he joined the San Francisco Fire Department, where he received recognition for rescuing a woman and her baby from a burning building. The local newspapers at the time referred to him as "an all-American boy."

In 1977, Dan White was elected to the San Francisco Board of Supervisors, representing District 8. This district included several neighborhoods near the southeastern parts of the city. His election came with strong support from police and firefighter unions. At that time, the supervisors were elected by district rather than citywide. White was a Democrat and he held a complicated stance on issues regarding gay rights. While he opposed some initiatives that targeted the growing gay community in San Francisco, he also voted against measures that would protect gay rights in housing and jobs.

During his time as a supervisor, Dan White had both allies and conflicts within the board. Initially, he worked well with Harvey Milk, who was the first openly gay person to hold public office in California. However, their relationship changed when they disagreed on community issues like the establishment of a facility for juvenile offenders in White's district.

On November 27, 1978, Daniel James White entered San Francisco City Hall with a Smith & Wesson Model 36 revolver and 10 rounds of ammunition. He had a plan to kill several politicians, including Mayor George Moscone and Supervisor Harvey Milk. To avoid security measures, White climbed through a basement window instead of using the front entrance.

Once inside, he went to Moscone's office and asked to be reinstated as supervisor. When Moscone refused, White shot him multiple times. Afterward, White moved to Milk's office, reloaded his gun, and shot Milk five times, with the gun pressed against Milk’s head for the last two shots.

After the shootings, White fled City Hall and went to the Northern Police Station, where he turned himself in. He confessed, saying, "I just shot him."

During his trial, White's defense claimed he was depressed and not capable of premeditated murder. His lawyers presented evidence that he had changed his eating habits, which became known as the "Twinkie defense." Despite emotional testimonies, the jury convicted him of voluntary manslaughter, and he was sentenced to seven years in prison.

White served five years before being paroled on January 7, 1984. After his release, he faced public backlash and concerns for his safety, leading to him being secretly moved to Los Angeles. He eventually returned to San Francisco.

On October 21, 1985, less than two years after his release, White committed suicide in his garage using carbon monoxide poisoning. He was buried with a government-issued headstone honoring his service as a war veteran, leaving behind his wife and three children.