International environmental law (IEL) has been unable to respond effectively to the Anthropocene’s global socio-ecological crisis, which is critically existential and requires radical interventions and regulatory reform. This article explores the potential of the recent United Nations (UN)-backed initiative to adopt a Global Pact for the Environment as an opportunity to reform IEL. It does so by (i) reflecting on the Anthropocene’s demands for a constitutionalized form of IEL through the lens of global environmental constitutionalism; (ii) investigating the extent to which the Global Pact could contribute to such a vision; and (iii) suggesting ways in which to strengthen the constitutional potential of the Global Pact in this endeavour. To this end, the article revisits the World Charter for Nature of 1982, which seems to have slipped off the radar in academic as well as policy circles. A case is made for renewed support of the Charter – which already enjoys the backing of the majority of UN General Assembly member states, and which has constitutional qualities – to serve as a ‘best-practice’ example during the ensuing negotiation of the Global Pact.