The article considers implications of contested multilateralism for the processes and normative standards of global constitutionalism. The focus is primarily on aspects of CM regarded as a mode of constitutional change, considering what to make of such a form of ‘extra-constitutional’ procedure. Research challenges for political science, law and normative political theory are identified. Challenges by CM to the stability of international law are argued to be overdrawn. Of greater concern is that CM lends itself to piecemeal adjustments rather than reforms with an eye to the systemic effects. However, these worries must be tempered by the non-ideal nature of the present legal structure which should make us wary of imposing normative standards drawn from settings where institutions are fully just and generally complied with.