In this article, we theorize and develop a posthumanist and new materialist approach to sustainable development policy. We trace a humanist and anthropocentric emphasis in policy discussions of ‘sustainable’ development that reaches back almost 50 years, and still underpins recent United Nations (UN) statements. This UN approach has tied policies to counter environmental challenges such as anthropogenic climate change firmly to sus-taining and extending future human prosperity. By contrast, we chart a path beyond humanism and anthropocentrism, to establish a posthumanist environmentalism. This acknowledges human matter as an integral (rather than opposed) element within an all-encompassing ‘environment’. Posthumanism simultaneously rejects the homogeneity implied by terms such as ‘humanity’ or ‘human species’, as based on a stereotypical ‘human’ that turns out to be white, male and from the global North. Instead, ‘posthumans’ are heterogeneous, gaining a diverse range of context-specific capacities with other mat-ter. Some of these capacities (such as empathy, altruism, conceptual thinking and model-ling futures) are highly unusual and – paradoxically – may be key to addressing the current crises of environmental degradation and anthropogenic climate change.