Southend-on-Sea City Council, formerly known as Southend-on-Sea Borough Council, is the local authority for the unitary authority of Southend-on-Sea in Essex, England. Until 1 April 1998 it was a non-metropolitan district.
A by-election occurs when seats become vacant between council elections. Below is a summary of by-elections from 1983 onwards. Full by-election results are listed under the last regular election preceeding the by-election and can be found by clicking on the ward name.