This study investigates the impact of strategic purchasing on purchasing performance in the presence of a mediating impact of supplier development with a special reference to Sri Lankan apparel sector. This study also examines how supplier involvement mediates the relationship between strategic purchasing and supplier development. A theoretically grounded conceptual model is proposed and empirically tested using structural equation modeling approach. Data collected from a random sample of 85 apparel sector firms located in the Western Province in Sri Lanka are used to test the proposed model. Findings reveal that all hypotheses tested in the model are supported. Thus, this study concludes that supplier development acts as a partial mediator to boost the positive impact of strategic purchasing on the purchasing performance of the buyer firms. It is also evident from the findings that the supplier involvement partially mediates the relationship between strategic performance and supplier development. Ultimately, this study helps the management of Sri Lankan apparel sector firms to better understand how to uplift the purchasing function and increase its role in the firm for better performance.