Awami League-sponsored candidate bagged the chairman post in the election Hizla upazila, Barisal on Thursday after polling was completed.
Opposition BNP boycotted the election and have called hartal for the upazila for Sunday.
Barisal Returning Officer Dulal Talukder declared Awami League-sponsored candidate Sultan Mahmud Tipu the winner after votes were completed in the three postponed centres.
BNP-backed candidate Dewan Shahidul Islam alleged rigging and boycotted the poll. Local BNP called a hartal in the upazila for Sunday in protest to the poll outcome.