This article addresses the question of how we should understand the normative grounds of legitimacy in global governance institutions, given the social and organizational pluralism of the contemporary global political order. We argue that established normative accounts of legitimacy, underpinning both internationalist and cosmopolitan institutional models, are incompatible with real-world global social and organizational pluralism, insofar as they are articulated within the parameters of a ‘statist’ world order imaginary: this sees legitimacy as grounded in rational forms of political agency, exercised within ‘closed’ communities constituted by settled common interests and identities. To advance beyond these statist ideational constraints, we elaborate an alternative ‘pluralist’ world order imaginary: this sees legitimacy as partially grounded in creative forms of political agency, exercised in the constitution and ongoing transformation of a plurality of ‘open’ communities, with diverse and fluid interests and identities. Drawing on a case study analysis of political controversies surrounding the global governance of business and human rights, we argue that the pluralist imaginary illuminates how normative legitimacy in world politics can be strengthened by opening institutional mandates to contestation by multiple distinct collectives, even though doing so is incompatible with achieving a fully rationalized global institutional scheme.