<p>This study investigates the impact of board demographic attributes on the environmental disclosure by the non-financial listed firms for eight years (2016–2023). It also examines the moderating effect of institutional investors on such a relationship. The study data was obtained from 83 selected non-financial listed firms in Nigeria. The study uses content analysis techniques for environmental issues disclosed using the latest Global Reporting Initiatives standards from the sampled firms. The study used the generalized method of moments (GMM) econometric model to evaluate the direct effects of the board demographic attributes on firm environmental disclosure. Panels corrected standard errors (HPCSE) and feasible least squares (FGLS) regressions were used to establish the robustness of the GMM regression results. The findings reveal that board nationality and institutional ownership significantly increase environmental disclosure. In contrast, board gender diversity and board age have an insignificant positive relationship with environmental disclosure. Concerning moderation, institutional ownership has changed the relationship to negative, yet statistically positive, in the case of board gender diversity. This study utilized only three demographic characteristics and institutional ownership as a moderator, which are believed to influence environmental disclosure. Besides, it covered only eight years between 2016 and 2023. The findings reveal how board demographic attributes are constrained by institutional ownership to disclose environmental information. The findings would help policymakers and regulators in revising policies and regulations that can improve the ability of such attributes to help firms improve the level of reporting environmental information and economic stability. This study provides empirical evidence on how institutional investors used their power to prevent women, young directors and foreign directors on the board from making firms report environmental information in the annual reports Moreover, the study’s findings would contribute to the knowledge economy in a broader context, as environmental sustainability is one of the key objectives of the knowledge economy. Hence, the findings would assist policymakers in ensuring that the skills, knowledge, and experiences of board members are effectively utilized to improve environmental disclosure through effective policies. </p>