Over the past two decades, the global issue of modern slavery has become increasingly prominent within development thinking and practice. Efforts to address it largely focus on criminal prosecutions of immediate ‘perpetrators’, for instance those who are direct employers or middlemen. This article adds to a growing call from critical scholars to look to the structural drivers of such highly exploitative labour relations. Drawing on an unfree labour approach that views debt bondage as embedded in and reproduced by capitalist accumulation, this analysis explores the diffuse drivers of unfree labour through the experiences of indebted farmers who have migrated from rural areas to work in and around Phnom Penh as debt-bonded brick-kiln labourers. The study demonstrates how debt discipline in the context of unregulated microfinance lending in rural Cambodia creates the conditions for unfree labour to emerge. Evidencing links between risky lending practices and unfree labour, the article strengthens calls to understand modern slavery as unfree labour and, in doing so, highlights the failures of the UN’s Sustain- able Development Goal 8 and other similar policies to make these crucial connections.