This article revisits Jürgen Habermas’s long-lasting engagement with the tradition of natural law and argues that his work is unique in the contemporary context because it takes place without seeking to sever all possible connections to natural law. Its goals are then twofold: on the one hand, the article reconstructs what Habermas understands by natural law in order to account for its wider relevance as an intellectual resource in modern social theory; on the other, it reassesses the natural law elements that still reside in Habermas’s own thinking. In terms of structure, the article starts by revisiting Habermas’s definition of natural law and its role in modernity’s claim to normative self-foundation. The second section focuses on the role Habermas gives to sociology as the discipline through which the theory of communicative action was systematically elaborated. Being simultaneously an empirical approach and a normative theory of modern society, the sociological tradition is reconstructed in connection rather than in opposition to natural law. The last part turns to the universalistic foundations of Habermas’s social theory as way of recovering its moment of ‘unconditionality’. As they centre on the question of universalism, all three sections come together in the idea that Habermas’s social theory be depicted as postmetaphysical natural law.