Elections to Southend-on-Sea Borough Council took place on 6 May 2021. This was on the same day as other local elections across the United Kingdom. The results saw the Conservatives and Labour pick up seats at the expense of the local Independents.
The council is elected by thirds, so a single member was elected from all 17 wards to a term of four years. The seats elected at this election were last contested in 2016, however due to the COVID-19 pandemic the 2020 elections were delayed for 12 months.
The "rainbow coalition" between Labour, the Liberal Democrats and local independents continued in office, with Labour councillor Ian Gilbert being elected leader of the council.
Directly after the 2019 election the composition of the council was:
Prior to the election the composition of the council was:
After the election, the composition of the council was:
No UKIP candidate as previous (-11.5).
No Independent candidate as previous (-12.0).
No Independent candidate as previous (-14.1).
No UKIP candidate as previous (-11.1).