William Francis Galvin (born September 17, 1950) is an American politician who has served as the 27th Massachusetts secretary of the commonwealth since 1995. A member of the Democratic Party, he previously served in the Massachusetts House of Representatives from 1975 to 1991.

Galvin was born and raised in the Brighton neighborhood of Boston. He attended Saint Mary's High School in Waltham, Massachusetts and graduated in 1968. Galvin graduated cum laude from Boston College in 1972 and received a Juris Doctor from Suffolk University Law School in 1976.

Galvin began his political career in 1972 as an aide to the Massachusetts Governor's Council after graduating from Boston College, thanks to his connection with councilor Herb Connolly, whom Galvin had campaigned for. Galvin worked part-time at the council while attending Suffolk Law School full-time. Galvin won a special election to the open seat in the Massachusetts General Court in 1975, after State Representative Michael Daly departed from office; the race had nine candidates. Galvin became the Massachusetts state representative from the Allston-Brighton district, the same year he graduated from law school. He was the Democratic nominee for Massachusetts State Treasurer in 1990, but was defeated by Republican Joe Malone. It was during this election that he was given the nickname "The Prince of Darkness", in reference to his habit of working late into the night and making legislative deals behind closed doors. He was first elected Secretary of the Commonwealth in 1994, and has retained this title longer than any other politician in Massachusetts history.

Galvin has been an active participant in the National Association of Secretaries of State, serving first as Chairman of the Standing Committee on Securities, then as co-chairman of the Committee on Presidential Primaries.

At one point during the administration of Gov. Mitt Romney and Lt. Gov. Kerry Healey, Galvin became the Acting Governor of Massachusetts when both Romney and Healey were out of the state. During the administration of former Acting Governor Jane Swift, Galvin automatically became Acting Governor whenever Swift left the state, since there was no lieutenant governor in office at the time. When Swift gave birth to twins in 2001, she chose to keep full executive authority and did not hand over the governorship at any point to Galvin.

While it had been widely rumored that Galvin would run for Governor of Massachusetts in 2006 as a Democrat, he announced at the end of 2005 that he would instead seek reelection as Secretary of State. Voting rights advocate John Bonifaz had already declared that he would run for the office, and stayed in the race to challenge Galvin for re-election. However, Galvin defeated Bonifaz in the September 19 Democratic primary. Galvin defeated Green-Rainbow Party candidate Jill Stein, a medical doctor and environmental health advocate who ran for Governor in 2002, in the November general election.

The Democratic primary race received relatively little attention or press coverage for most of 2006, but in the last few weeks before election, a controversy over Galvin's refusal to debate his opponent broke into the news with a front-page story in The Boston Sunday Globe. This is the first time a front-page story appeared about this race in any major Boston paper.

In November 2017, Boston City Council member Josh Zakim announced that he would run for Secretary of the Commonwealth, challenging fellow-Democrat Galvin in the 2018 election. Amid the primary challenge, Galvin came out in favor of same-day voter registration and automatic voter registration. Previously, Galvin had expressed skepticism of automatic voter registration, and had appealed a Superior Court ruling which struck down a state law requiring that voters be registered 20 days prior to an election in order to vote in it. On June 2, 2018, Zakim won the endorsement of the Massachusetts Democratic Party at its state convention, defeating Galvin with 55% of the vote to Galvin's 45%. Galvin subsequently defeated Zakim in the Democratic primary on September 4 with 67% of the vote. On November 6, Galvin won re-election as Secretary of the Commonwealth, winning 71% of the vote against Republican Anthony Amore.