This study investigates the impact of the Sustainable Growth Rate (SGR) on National Pension Service (NPS) ownership and firm value among Korean listed firms, while further examining the moderated mediation effect of ESG ratings within this relationship. Using a balanced panel dataset, the empirical analysis demonstrates that SGR has a significant positive direct effect on firm value, suggesting that firms with stronger financial growth capacity and greater financial autonomy receive higher market valuations. The findings further indicate that SGR significantly increases NPS ownership, and that NPS ownership positively affects firm value while partially mediating the relationship between SGR and firm value. Moreover, ESG ratings strengthen this mediating mechanism through their interaction with SGR, indicating that the indirect effect of SGR on firm value through NPS ownership is more pronounced for firms with higher ESG ratings. These findings suggest that SGR and ESG should be viewed as complementary dimensions of corporate investment evaluation rather than independent indicators. From both theoretical and managerial perspectives, the results underscore the importance of integrating financial and non-financial performance into sustainable corporate strategies, thereby facilitating responsible investment by the National Pension Service and enhancing long-term firm value.