Miguel Sanchez, 34, died Friday afternoon from the H1N1 virus.
Family members said they believe he contracted it while campaigning door to door.
Sanchez was running in the city's special election to replace former Councilman Luis Artiga, who resigned last fall amid allegations that he and other city officials misappropriated public funds.
For many, Sanchez was the new face of change for the embattled city of Bell.
Sanchez was among the many angry residents who protested outside Bell City Hall last summer, demanding the resignations of city officials who were receiving outsize salaries.
Several people had gathered at his home to attend a rosary and pay their respects.
"He went ahead and fought for what he believed in until the very end," said Sanchez's brother, George. "Him being ill due to diabetes, it had much more of an impact than any other regular person.
"Even though he's gone, he's still with us. People tell me, 'You know what? I'm still going to vote for him.' That would mean a lot."
A procession and candlelight vigil was held starting from the Sanchez family's home and ending at Bell City Hall.
Hundreds of friends, family and supporters sang songs as they marched.
The Associated Press contributed to this report.