The 2003 San Francisco mayoral election occurred on November 4, 2003. The incumbent, Willie Brown, was termed out of office and could not seek a third term. The general election included three top candidates including then Supervisor Gavin Newsom and then President of the Board of Supervisors, Matt Gonzalez and former Supervisor Angela Alioto. No candidate received the required majority so the race went into a run-off of the two top candidates, which were Gavin Newsom and Matt Gonzalez. The run-off occurred on December 9, 2003 where Gavin Newsom was elected mayor of San Francisco.
Municipal elections in California are officially non-partisan, though most candidates in San Francisco do receive funding and support from various political parties.
In 2003, then-Supervisor Gavin Newsom, a Democrat, ran in a large field of challengers, including Board of Supervisors President Matt Gonzalez, Supervisor Tom Ammiano, former Supervisor Angela Alioto, city Treasurer Susan Leal, and former Police Chief Tony Ribera. Newsom and Gonzalez took first and second place, respectively, but neither won a majority, so the two advanced to a runoff election. The election gained international attention, and third party advocates saw it as a chance to dethrone the Democratic Party.
Newsom ran as a moderate against leftist/progressive Gonzalez, a member of the Green Party. It was the first mayoral election in San Francisco that a Green Party candidate took a noticeable amount of the vote. Had he won, Gonzalez would have been the most prominent elected Green Party member in the United States. The election was close, with Gonzalez leading in the polls and winning the popular vote among ballots cast on election day, while Newsom had a larger lead on absentee ballots.