Knowles — who rode out weeks of unrest after Brown, an unarmed teenager, was shot and killed by Ferguson police Officer Darren Wilson — defeated City Council member Ella Jones 56 percent to 44 percent, with all of the city's 13 precincts reporting. Jones, 62, would have become the first black mayor in the city's 122 years had she been elected.
Tuesday's election — the first chance that voters had had to weigh in since the nationally followed shooting — also came on the same day that U.S. Attorney General Jeff Sessions called for a review of court-ordered criminal justice reforms demanded by the Obama administration in Ferguson and numerous other cities.
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Knowles, 37, is white. Like Jones, he campaigned on a promise to continue the changes and reforms instituted following a scathing report by the Justice Department, which accused police and the courts of systemic bias against poor black residents.
Ferguson is one of the smallest cities in the country to have negotiated a consent decree with the federal government, and both candidates were mindful that any delay could undermine fragile efforts to create trust between the police department and skeptical segments of the community.
Ferguson's mayor has less power than the city manager, but given the city's recent history and its place in the national spotlight, the mayor has enormous power to shape public perceptions as the "face" of the city.
The fear now, with Knowles' winning a third three-year term, is that residents, activists and protesters — already doubtful that anything will ever change — could harden their attitudes.
But Knowles argued that his experience would be valuable guiding the city through a period of reform over the next three years with new council members, a new police chief and a new city manager.
Voters also overwhelmingly approved a measure to require police officers to wear body cameras at all times and to require the city to keep body camera video for at least two years.
Ferguson officers have used the cameras since Brown was killed, but critics accused police of not wearing them consistently.
Ron Allen is an NBC News correspondent based in New York.
Alex Johnson is a senior writer for NBC News covering general news and technology and religion. He is based in Los Angeles.