This Ph.D. thesis investigates the deployment in European non-discrimination law of a range of critical theoretical insights commonly understood under the term ‘intersectionality’. In equality law, intersectionality and related critical repertoires mobilise external (mainly sociological) scientific discourses about the multidimensionality and complexity of inequalities to expose how the categorical understanding of disadvantage prevailing in non-discrimination law excludes from its scope of protection certain minority groups situated at the crossroads of several axes of inequality. While legal scholars have deplored the lack of consideration for the intersectionality critique in judges’ dealings with discrimination and have normatively applied intersectionality to argue what non-discrimination law and doctrine ought to be, little research has been conducted into how various legal participants actually seize and operationalise intersectionality. Combining critical legal theory with a socio-legal approach, this thesis proposes to fill this gap by offering a ‘law in action’ account of the mobilisations of the intersectionality critique by legal participants in three main sites: advocacy and the law-making process; litigation and the framing of legal claims; and doctrine and judicial reasoning. It focuses on two case studies: the non-discrimination law regimes of the European Union and the Council of Europe. The aim is to understand how and why legal actors operate intersectionality as a critical and transformative frame in European nondiscrimination law and how these discursive mobilisations impact the legal protection of equality. This thesis thus explores the role of various epistemic workers, norm entrepreneurs and legal engineers in translating, elaborating, diffusing and operating intersectionality in European nondiscrimination law. It exposes how these actors seek to shift the core legal analytical and hermeneutical tenets of the non-discrimination doctrine to expand existing legal opportunities for equality claims. Finally, this dissertation shows how judges’ response to intersectionality has extended the boundaries of non-discrimination rights in European equality jurisprudence.