The increasing importance of sustainable behaviour in business has enhanced its impact on supply chain management. Firms foster sustainability in their supplier base in reaction to growing sustainability requirements in various ways, including sustainable supplier co-operation. Knowledge about the effects of sustainable supplier co-operation on firm performance is limited; therefore, this study tests antecedents and implications of sustainable supplier co-operation according to the triple bottom line. A survey of Western European firms reveals that sustainable supplier co-operation has generally positive effects on firm performance across social, green and economic dimensions. However, only green practices have positive significant effects on economic performance, not social practices (e.g., child labour rules). In contrast to practitioner perceptions, investments in sustainability, for example through sustainable supplier co-operation does indeed result in sufficient returns.