‘Modern slavery’ describes various forms of severe relational labour exploitation. In the realm of global value chains and global factories that are led by multinational enterprises, modern slavery encompasses practices such as forced labour and debt bondage. Multinational enterprises organise and orchestrate global value chains into global factories that are highly adaptive to market pressures and changes in the external environment. We employ the global factory framework to conceptualise when and how global value chains become more vulnerable to modern slavery. We argue that combinations of the three global value chain characteristics: complexity, appropriation arrangements, and obligation cascadence, jointly form an environment in which modern slavery can evolve and take root. The degree to which forms of modern slavery become visible and recognisable depends on the particular combination of these characteristics. External factors can moderate the relationship between these factors (e.g. involvement of non-governmental organisations) or exaggerate their effect (e.g. a pandemic).