In San Francisco, the election for the eighth district member of the board of supervisors was also on the ballot.

[1] All four main candidates identified as Democrats, though the position is officially nonpartisan per the Constitution of California.

Ed Lee, who was appointed mayor of San Francisco in 2011 following Gavin Newsom's election as lieutenant governor of California, elected to a full term in 2011, and reelected in 2015, died of cardiac arrest on December 12, 2017.

[5] London Breed, the president of the San Francisco Board of Supervisors, became the city's acting mayor.

[6][7] On January 23, 2018, the board of supervisors selected Mark Farrell to serve as interim mayor until the special election could be held.

Citing Ron Conway's role as a benefactor to Breed, Supervisors Aaron Peskin and Jane Kim, considered the progressive members of the board, sought to deny Breed the benefits of incumbency going into the election.

[62][63] On June 13, with only 8,000 ballots left to count,[64] Leno conceded defeat and congratulated Breed on her victory.