The First World War saw an unprecedented expansion of the executive powers of the British government that radically changed the relationship between individual citizens and the state. This article offers a new perspective on these developments by analysing the activities of the National Council for Civil Liberties (NCCL) between 1916 and 1918. It explores the emergence of civil liberties activism in Britain during the war and its impact on British political culture. The NCCL became an efficiently organised pressure group, campaigning against press censorship, political policing and the suppression of anti-war dissent. This article argues that the innovative campaigning and propaganda methods used by the NCCL mark a moment of innovation that can be described as a revolution in activism. It represents a shift from the grass-roots political associations of the nineteenth century towards more professional forms of political activism that foreshadowed the rise of modern pressure groups and NGOs. The article also explains the emergence of a new discourse about the relationship between civil liberties, democracy and socialism in Britain during the First World War. The NCCL became an important locus for the networks of protest and dissent that emerged in Britain in response to the expansion of the wartime state. The article thus presents a new perspective on the beginnings of civil liberties activism in Britain and the impact of the First World War on its political culture.