The 1963 Bristol South East by-election was a by-election held on 20 August 1963 for the British House of Commons constituency of Bristol South East in the city of Bristol.
The seat had become vacant in 1961 when the constituency's Labour Member of Parliament (MP) Tony Benn had inherited a hereditary peerage from his father, becoming Viscount Stansgate and ineligible to serve in the House of Commons. Benn had first been elected at a by-election in 1950 and was re-elected in the next three general elections (the last with 56% of the votes). He stood in the 1961 by-election anyway and won 69.5% of the votes, but due to his known ineligibility, the Conservative Party candidate Malcolm St Clair challenged the result and was declared the winner by the election court over Benn's objections.
When the Peerage Act 1963 changed the law to allow Benn to renounce his peerage, St Clair resigned his seat by being appointed Crown Steward and Bailiff of the Manor of Northstead, triggering the 1963 by-election. The Conservatives did not nominate an official candidate, making this the last by-election in Great Britain in which there was no Conservative candidate until the Batley and Spen by-election in 2016, and the last by-election in Great Britain where the Conservatives did not field a candidate in a held seat until the Richmond Park by-election in 2016. Benn won again, with nearly 80% of the votes.