As a key microeconomic subject in the market, enterprises play a decisive role in achieving the national “dual carbon” goals and promoting the green and low-carbon development of the economy and society. In recent years, ESG rating, as an informal environmental regulation system, through the participation of the third-party public, has a significant impact on enterprises’ environmental behavior with soft constraints and hidden pressure, which is more effective in stimulating enterprises’ carbon reduction efforts and can effectively promote enterprises’ green and low-carbon transformation. However, existing literature mostly focuses on the economic benefits of ESG ratings, with limited research on their impact on corporate environmental performance, especially from the perspective of informal environmental regulation. Based on data from A-share listed companies from 2010 to 2022, this paper estimates the carbon emissions of enterprises by using the carbon emission data at the industry level and constructs a multi-period difference-in-differences (DID) model using the event of the first publication of ESG ratings by Shangdaoronglv. The empirical results show that ESG ratings have a significant carbon emissions reduction effect, which remains robust after a series of robustness tests; Mechanism analysis indicates that ESG ratings can restrain corporate short-sightedness, ease financing constraints, and promote green innovation, thereby reducing corporate carbon emissions; Heterogeneity tests reveal that the impact of ESG ratings on carbon emissions varies significantly across firms with different ownership structures, levels of digitalization, and environmental attributes; Moderating effect analysis shows that the peer effect of ESG ratings strengthens their carbon emissions reduction effect, while ESG rating divergence weakens this effect. Compared with previous literature, this paper expands on the following three aspects: First, it enriches and deepens the research perspective on corporate carbon emissions. Unlike prior studies that examined the environmental effects of ESG ratings from the perspective of market soft regulation, this paper explores the impact of ESG ratings on corporate carbon emissions within the framework of informal environmental regulation and corporate environmental behavior. It helps address the dual failures of the market and government in environmental protection and provides new empirical evidence for enhancing corporate responses to carbon emissions reduction through ESG ratings. Second, it verifies the mediating role of inhibiting corporate short-sightedness, alleviating financing constraints and promoting green innovation in the impact of ESG ratings on corporate carbon emissions, and comprehensively reveals how ESG ratings directly and indirectly affect corporate carbon emissions from the three dimensions: management, finance, and technology, which makes an important supplement to the mechanism of ESG ratings on corporate environmental behavior. Third, the heterogeneity of the impact of ESG rating on corporate carbon emissions is analyzed from the dimensions of different property rights, digital degree and environmental protection attributes, and the moderating effect of ESG group effect and ESG rating divergence on the carbon emission reduction effect of ESG rating is investigated, which provides a new research perspective and ideas for the systematic and comprehensive study of the role and value of ESG rating in corporate carbon emission reduction, and provides a theoretical basis and empirical evidence for enterprises to implement the responsibility of carbon emission reduction in ESG practice. The research conclusion of this paper provides a new perspective for the exploration of enterprise carbon emission reduction in theory and provides empirical evidence for the construction and improvement of enterprise sustainable development system in practice, which is of great significance for enterprises to actively fulfill their social responsibilities and promote China’s green transformation.