Learning processes play a crucial role in the development of the transformative capacity of social innovation actors. This article builds on the recently developed Transformative Social Innovation (TSI) theory to propose a conceptual framework and research agenda for understanding and investigating the roles and limits of network leadership in supporting learning processes that serve to develop the transformative capacity of social innovation. This focus on network leadership is underdeveloped so far in TSI theory. Addressing this research gap also serves to increase the practical relevance of TSI theory to practitioners engaged in network leadership. After presenting a synopsis of TSI theory, we present an overview of the elements of the conceptual framework, which are successively specified throughout the article. First, transformative change is conceptualized, involving three institutional dimensions: depth, width and length. Based on this, a definition of transformative capacity is proposed that addresses change across these three dimensions. We then describe how various types of learning processes can contribute to the development of transformative capacity. Next, we outline the roles of network leadership in supporting these learning processes across various network levels. We conclude with a research agenda for empirically investigating these roles of network leaders as agents for advancing transformative changes for sustainability.