Improving the supplier’s capabilities and relationships with the buyer to improve triple-bottom-line outcomes for multiple actors in the supply chain (including the suppliers and buyers) is the very purpose of sustainable supplier development. We apply the concept of sustainable supplier development in an agri-food context in a developing economy. The study aims to create a theoretical framework that explains how initiatives by buyers (often processors in the agri-food industry) to develop farmers can result in sustainable farmer performance. Collectively, the propositions derived by us via a literature synthesis propose that farmer development leads to farmer capability development and improved relationships (with the buyer), enabling the farmer to achieve sustainable performance (i.e., performance in economic, social, and environmental domains). The importance of the study from a theory building perspective is that the study attempts to reconcile the supply chain management literature on supplier development in tangible goods manufacturing with the agribusiness literature in developing economies whether or not the farmer occupies the bottom of the income pyramid. The study is also important to academia and policymakers because it acts as a forerunner for the further development of the theoretical model and its testing with a large sample of data to interpret what the results imply from practical and theoretical standpoints.