London Breed became the first African-American woman elected to lead San Francisco on Wednesday, when her opponent conceded a tight race.
Breed will serve until 2020, finishing the term of the late Mayor Ed Lee, who died in December at age 65.
At a short news conference, Breed praised Lee and thanked her supporters, as well as the other candidates, including Mark Leno, a former state senator who conceded the race hours earlier. She struck an optimistic tone about the city's future.
"I am London Breed, I am president of the San Francisco Board of Supervisors, and soon to be mayor of the city and county of San Francisco," she said to cheers.
Breed said: "I am so hopeful about the future of our city, and I am looking forward to serving as your mayor. I am truly humbled and I am truly honored."