The present study aims to investigate the moderating role of good governance in the effect of Human Development Index (HDI) on carbon dioxide (CO₂) emissions in selected OPEC member countries. For this purpose, annual data covering the period 2002–2022 were collected. To test the research hypotheses, the Generalized Method of Moments (GMM) was employed to control for endogeneity, and the Panel Threshold Regression (PTR) model was applied to examine nonlinear relationships. The findings indicate that the effect of human development on CO₂ emissions depends on the level of good governance and follows a nonlinear threshold pattern. The estimated threshold value for good governance was −0.0320 at the 95% confidence level. In the below-threshold regime (weaker governance conditions), an increase in HDI leads to a positive and statistically significant increase in CO₂ emissions, with an estimated coefficient of 5.94 (P<0.05). In contrast, in the above-threshold regime (stronger governance conditions), human development exerts a negative and statistically significant effect on CO₂ emissions, with an estimated coefficient of −48.97 (P<0.05). The findings suggest that good governance plays an effective role in reversing the impact of human development on carbon emissions, and improvements in institutional quality can create the conditions for reducing environmental pressures.