Abedin Sarudson, 40, was shot dead by a gunman in Parang town, earlier identified as a "hot spot" for election-related violence.
Inspector Sam Isnain, municipal police chief, said Sarudson was killed on the spot, adding that he believed the attack could have been politically motivated.
In January, 22 people were killed when a bomb targeting Parang Mayor Vivencio Bataga exploded inside a packed sports stadium.
Elections in the Philippines are often marred by violence at the local level with some politicians using "private armies" of supporters to intimidate voters. — AFP