Dakar Mayor Barthelemy Dias, a fierce opponent of President Macky Sall, had sought to overturn the sentence for the 2011 killing of a wrestler named Ndiaga Diouf during a rally that turned violent.
In a politically-charged case, the court upheld the six-month prison term and 18-month suspended sentence.
The court "confirms the judgement in all its provisions, dismisses the civil party in all its requests", the presiding judge said.
Dias, 46, was elected city mayor in February, riding a wave of support for leading opposition figure Ousmane Sonko, and there is speculation that he himself has presidential ambitions.
Police deployed in and around the courthouse and anti-riot vehicles were placed at key intersections of the capital.
Dias' lawyer Demba Cire Bathily said he would advise his client to lodge an appeal in cassation.
"The major implication is that his mayoral mandate isn't threatened," the lawyer said.
The implications for Dias' mandate as a parliamentarian were not an issue since "the decision isn't final", he added.
Dias was sentenced in 2017 to a six-month prison term and 18 months' suspended in a trial in which he appeared alongside a dozen other defendants.
His appeal began in March after having been postponed several times.