The 1961 Bristol South East by-election was a by-election held on 4 May 1961 for the British House of Commons constituency of Bristol South East in the city of Bristol.
The seat had become vacant when the constituency's Labour Member of Parliament (MP), Tony Benn, had inherited a hereditary peerage from his father and became Viscount Stansgate, thus making him automatically ineligible to serve in the House of Commons. He had been elected at a by-election in 1950.
Benn stood in the by-election anyway—claiming that he had not asked for and would not ask for a writ of summons to the House of Lords—and won the majority of votes, but he was forbidden by Parliamentary authorities to physically return to the Commons due to his ineligibility. The Conservative Party candidate Malcolm St Clair—who was himself the heir to a peerage—filed a petition against the result, and was declared the winner after a court challenge.
When the law was later changed by the Peerage Act 1963 to allow Benn to renounce his peerage, Benn immediately did so and, fulfilling a promise to the electors of Bristol South East, St Clair resigned his seat. Benn was returned to the House of Commons at the 1963 Bristol South East by-election, which was not contested by the Conservatives.