Brendan Donnelly studied classics at Oxford University before joining the Foreign Office. He then worked for the Conservative Group in the European Parliament and himself served one term as an elected member of the European Parliament. He left the Conservative Party at the turn of the century in protest against its anti-European policies.

After leaving the European Parliament, Brendan Donnelly became Director of the Federal Trust, a research institute concerned with questions of global and particularly European governance. He has written and broadcast extensively on the institutional structures of the EU, both before and after Brexit. He retired as Director of the Federal Trust in 2025, but continues as its Deputy Director and a member of its governing Council.