In recent years, humanitarianism has been portrayed as a revolutionary new force in the anti-nuclear movement. This article challenges this progressive understanding of humanitarianism’s role in nuclear affairs by exploring how the language and concept of humanitarianism have been deployed by two states that have been deeply involved in international nuclear law projects over the last 50 years: Australia and New Zealand. It argues that contrary to popular perceptions about the radical potential of humanitarianism in nuclear affairs, the phenomenon’s track record in Australia and New Zealand is chequered. Indeed, in certain key respects, humanitarianism has impeded anti-nuclear agendas in Australia and New Zealand: first, the ambiguity inherent in the language of humanitarianism has allowed it to be deployed to support the maintenance of nuclear weapons; and secondly, humanitarianism has generated outcomes that often support and reinforce the status quo legally and structurally. The article also offers some reflections on the relationship between humanitarianism and international law in the nuclear context. Specifically, it shows how the Australian and New Zealand case studies reveal contradictory approaches to, and understandings of, humanitarianism as law.