London Breed, San Francisco’s first Black woman mayor who steered the city through the pandemic but also saw its quality of life sink, conceded her re-election race on Thursday.

Ms. Breed posted on social media that she had called Daniel Lurie, an heir to the Levi Strauss fortune who has never held elected office, to congratulate him on his win.

“Being mayor of San Francisco has been the greatest honor of my lifetime,” she wrote on X. “I’m beyond grateful to our residents for the opportunity to serve the city that raised me.”

The Associated Press had not yet called the race, though local news outlets did.

Mr. Lurie will take office in January, and Ms. Breed vowed on X that she would work to ensure a smooth transition. Both Mr. Lurie and Ms. Breed are Democrats and San Francisco natives who grew up mere miles from each other, he in luxury and she in poverty.

Mr. Lurie, the founder of an anti-poverty nonprofit, vowed during his campaign to improve public safety and city services for residents.

Ms. Breed’s concession came after multiple rounds of counting under the city’s ranked-choice voting system. Mr. Lurie cultivated support from various communities and particularly focused on appealing to Chinese American voters. He also made a concerted effort this fall to ask voters to list him as their second candidate if he was not their first choice, and he secured high ballot rankings from voters across San Francisco’s ideological spectrum.