In today's world, a sustainable approach to corporate governance can be a source of competitive advantage and a long-term success factor for any firm. Sustainable governance requires that the board of directors considers economic, social and environmental expectations in an integrated way, no matter what ownership structure and formal rules of corporate governance apply to the company: this mitigates the traditional differences between insider and outsider systems of corporate governance. Previous studies failed to consider the contribution of sustainability in the process of corporate governance convergence. Therefore, the aim of this article is to fill the gap in the existing literature by means of a qualitative analysis, supporting the international debate about convergence of corporate governance systems. The article describes the evolution of outsider and insider systems in the light of the increasing importance of sustainability in the board's decision-making and firm's operation to satisfy the needs of all the company's stakeholders. According to this, a qualitative content analysis developed with a directed approach completes the theoretical discussion, demonstrating that sustainability can bring de facto convergence between outsider and insider corporate governance systems. The article aims to be a theoretical starting point for future research, the findings of which could also have practical implications: the study encourages the policy makers to translate the sustainable business best practices into laws and recommendations, strengthening the mutual influence between formal and substantial convergence.