Current debates in Germany revolve around the matter of introducing a new legal form for companies that follows the principles of steward ownership, i.e., a firm that belongs to itself, to make firms more responsible and sustainable. However, this effect still lacks academic support. This study examines how steward ownership affects corporate sustainability governance by shedding light on how steward-owned firms approach setting up their sustainability strategy, structure for sustainability, external stakeholder management, and sustainability control in comparison to traditionally owned companies. The empirical study was carried out by means of twelve semi-structured interviews that were transcribed and analyzed according to the method of qualitative content analysis. Based on an analytical framework in the light of agency theory and stewardship theory, nine propositions are postulated and discussed. This paper finds the initial development of an organization’s sustainability strategy to be unaffected by its owner- ship structure. However, in comparison to traditionally owned firms, steward-owned firms are found to view sustainability more holistically, discuss decision-making for sustainability more critically, adopt systematic sustainability certifications of the whole organization more frequently, check sustainability measurements more critically, and attach less importance to formal corporate sustainability governance structures due to a strong purpose-orientation of the entire organization. Further, steward ownership has an indirect positive influence on employee motivation and empowerment, which can be considered a prerequisite and foundation of corporate sustainability governance. The findings of this study contribute to scholarly discussions on ways to make the business landscape more sustainable. Amongst practition- ers, the results of this study help to foster a new awareness for the importance of ownership structures of firms and the nature of the relationship between owners and managers, which can help promote com- prehensive, fertile corporate sustainability governance structures within companies.