The sustainability approach is currently a major concern and priority in the business world along with the increasing awareness of environmental, social, and governance issues, or commonly abbreviated as ESG. This study aims to analyze the effect of supervisory board effectiveness on corporate environmental and social performance and analyze the role of country-level governance and religiosity as moderating variables. The method used in this study is panel data regression analysis on non-financial companies in G7 countries and Indonesia for the period of 2017–2022, with principal component analysis (PCA) also used to reduce the various indicators of supervisory board effectiveness and country-level governance into one distinct composite index for each variable. The results show that an effective supervisory board can improve corporate social performance but has no significant impact on environmental performance. In addition, strong governance at the country level is shown to weaken the relationship between the effectiveness of the supervisory board and its environmental and social performance, while the level of religiosity in this case does not moderate the relationship of these variables. This study emphasizes the important role of country-level governance in optimizing the effectiveness of supervisory boards in supporting sustainability achievements and underlines the need for a more adaptive approach at both the firm and the government levels to improve sustainability performance.