["Corporate Social Responsibility and Environmental Management, Volume 33, Issue 3, Page 4383-4398, May 2026. ", "\nABSTRACT\nThis study examines how three core corporate governance mechanisms, board independence, institutional ownership, and CEO duality, drive ESG performance among 551 publicly listed firms in Malaysia, Singapore, Indonesia, and Thailand over the period 2015–2023 (4959 firm‐year observations). Using fixed‐effects panel regressions with two‐way clustered standard errors and year, country, industry, and firm fixed effects, the results show that board independence and institutional ownership are strongly and positively associated with ESG performance, whereas CEO duality has a significant negative effect. Board gender diversity not only has a direct positive impact but, more importantly, significantly moderates these relationships: It amplifies the beneficial effects of independence and institutional ownership and intensifies the detrimental effect of CEO duality. All governance, ESG linkages, and the moderating role of female directors are markedly stronger in Malaysia and Singapore, countries characterized by rigorous regulatory enforcement and gender‐diversity mandates, than in Indonesia and Thailand. Robustness tests employing random effects, outlier‐excluded subsamples, and a critical‐mass threshold (≥ 30% women directors) confirm the stability and even strengthen the findings. These results highlight that effective internal governance requires supportive institutional conditions and meaningful female board representation to deliver superior sustainability outcomes in Southeast Asia.\n"]