While there is a substantial body of research focused on the links between North-South trade and sustainable development, research on South-South trade and sustainable development is still in its infancy. Given current understandings of the drivers of sustainable development, one might expect increasing trade in agricultural commodities within the global South to have a negative impact on sustainable development opportunities. In this sense, the Ceylon tea industry presents a puzzle. Despite exporting most of its tea to Southern markets, it has been among the top performers in terms of economic, social, and environmental practices. As such, the case raises a number of questions around shifting trade patterns and their implications for sustainability outcomes. I address these questions through four propositions – three mechanisms and one condition – through which South-South trade can expand the opportunities for sustainable development. While the exact nature of sustainable development outcomes will ultimately be decided through domestic political struggles, shifts toward more equal trade can make sustainable production more likely. Overall, the analysis draws attention to nuanced ways in which end markets shape their respective supply chains and how these dynamics impact the potential for actors operating at the bottom of supply chains to shape sustainability outcomes.