Annabel Brett studied Classics at Cambridge before turning to the history of political thought for her PhD on subjective rights in later medieval scholastic thought, subsequently published as Liberty, right and nature by Cambridge University Press in 1997. After a research fellowship at Gonville and Caius College followed by a lectureship in Philosophy at the University of York, she returned to Cambridge in 1996 to take up a lectureship in History of Political Thought.

Currently Professor of Political Thought and History and a co-director of the Cambridge Centre for Political Thought, she has lectured and published widely in the history of late medieval and early modern moral and political thought, with an emphasis on the natural law tradition, Aristotelianism and scholastic philosophy. Her Carlyle Lectures of 2008 were published by Princeton University Press in 2011 as Changes of state. Nature and the limits of the city in early moder natural law. She is the author of a major new translation of Marsilius of Padua's The Defender of the Peace (2005) and retains a strong interest in the theory and practice of translation in history. More recently, she has turned her attention to the history of international law, resulting in several publications and a major collaborative project now published as Annabel Brett, Megan Donaldson and Martti Koskenniemi eds., History, politics, law. Thinking through the international (Cambridge University Press, 2021).