Brendan Patrick Donnelly (born 25 August 1950) is a British pro-European Union politician who has been the leader of Rejoin EU since 2024.

Donnelly previously served as the Member of the European Parliament (MEP) for the Sussex South and Crawley constituency from 1994 to 1999.

Born in London, Donnelly was educated at St Ignatius' College in Tottenham, and then at Christ Church, Oxford.

From 1986 to 1987, he was a political adviser to Lord Cockfield, and then from 1987 to 1990 worked as an independent consultant on the European Community.

He stood for Rejoin EU in the June 2021 Chesham and Amersham by-election, and also ran in Finchley and Golders Green (UK Parliament constituency) for the 2024 United Kingdom general election.