Through symptomatic reading, we analyze the visible and the invisible – the explicit and the implicit – in the works of Filipino international legal scholar Merlin Magallona (1934–2022). We argue that Magallona's international legal thought was rooted in Marxist theory and practice and honed through the mode of production debates in the Philippine communist movement during the 1960s. Specifically, he developed a critique of the neocolonial division of labour and produced a materialist reading of international legal doctrines through “Postcolonial Self-Determination” – a synthesis of the antinomy of positivism and self-determination. In practice, his Third World Marxism led him to support the NIEO and resist UNCLOS through constitutional litigation based on the imperialist Treaty of Paris of 1898. Magallona's critique and praxis suggest new forms of resistance to the new imperialisms and underscore the imperative of a practice turn in Marxist international legal theory.