While prior Information Systems and Operations Management literature emphasizes the role of both the firm's IT infrastructure and the general degree of competition as antecedents of firm performance, the organizational capabilities that mediate these important relationships remain undetermined. Responding to the increasing importance of incorporating environmental sustainability practices across the internal and external supply chain, this study proposes green supply chain management as an important mediator of the IT infrastructure/competitive aggressiveness–firm performance relationship. Enabled by internal IT capabilities and external competitive pressure, green supply chain management capabilities support firms in achieving operational excellence, thereby contributing to the firm's overall performance. Using primary and secondary data on 203 large firms in Spain, this study applies the partial least squares approach to structural equation modeling. Its empirical analysis reveals that green supply chain management fully mediates the relationships between IT infrastructure capability and firm performance, and competitive aggressiveness and firm performance, respectively.