This article presents an analysis of slave labour (as it is known in Brazil) among sugar cane workers within a globalising production network. It employs the Global Production Network (GPN) framework to argue that the dynamics of production networks are fundamental to the reproduction of unfree and degrading labour in this case. First, the power exercised by buyers is a key aspect of processes resulting in slave labour. Conversely, efforts to combat slave labour have been strengthened by acknowledging and working through this power. Second, the state exercises governance within the production network rather than only providing its institutional context. Beyond these dynamics, however, wider processes are involved in making labour available on particular terms and conditions. Third, then, processes of racialisation facilitate the imposition of restrictions on workers mobility, degrading conditions and intensification of work. Labour is, in other words, devalued. This implies that the ways in which competing judgments over value are resolved merit as much attention in GPN analysis as is currently given to the creation, enhancement and capture of value. I examine the case of slave labour among migrant Brazilian sugar cane workers. I use the GPN framework to place unfree labour within production networks. I show how labour is de-valued within a GPN through processes of racialisation. I show how beyond institutional context, the state exercises governance within GPNs. I show how efforts to combat slave labour work through GPN power dynamics.