The good performance of enterprise ESG (Environmental, Social, and Governance) is a crucial lever for promoting sustainable development and enhancing corporate image and overall value, thus achieving high-quality economic development. The regional peer effect refers to a phenomenon where, within a specific geographical area, certain management policies, culture, and regional economic development factors lead to a convergence in strategic choices, operational models, organizational culture, etc., among enterprises. However, there is limited literature addressing the regional peer effect of enterprise ESG performance, and its mechanisms and heterogeneous manifestations remain unclear. Based on data from A-share listed companies in the period from 2009 to 2021, this study empirically tests the existence, mechanisms, heterogeneity, and related consequences of the regional peer effect on enterprise ESG performance. The research reveals that there is a regional peer effect in enterprise ESG performance, and this conclusion is validated through a series of endogeneity and robustness tests, including instrumental variable methods, two-stage residual inclusion methods, placebo tests, substitution variables, and the inclusion of control variables. Information asymmetry, internal governance, external demonstration, and government regulation are identified as the causes of the regional peer effect in enterprise ESG performance. Specifically, information asymmetry increases the motivation for lower-information companies to learn and imitate the ESG performance of higher-information companies, thereby enhancing the regional peer effect. Lower internal governance levels make it difficult for companies to meet the requirements of scientifically deciding their ESG performance, promoting the motivation for companies to imitate the ESG performance of regionally peer companies, thereby increasing the regional peer effect. Positive external demonstration creates a favorable ESG learning atmosphere for companies, increasing the motivation for companies to learn and imitate the ESG performance of other companies, thereby increasing the regional peer effect. Government regulation leads to a certain convergence in ESG decision-making behavior among enterprises, thereby increasing the regional peer effect. Heterogeneity analysis reveals that when a company has a lower position in its region, it has a stronger motivation to learn and imitate regional leading companies, making the regional peer effect in ESG performance more pronounced. When a company is in a mature or declining phase, the regional peer effect in its ESG performance is more apparent, as it seeks to reduce decision-making risks. In contrast, companies in a growth phase are more inclined to engage in strategic exploration and innovation, resulting in a less pronounced peer effect. Non-heavy-polluting industries exhibit a more pronounced regional peer effect in ESG performance compared to heavy-polluting industries. Further research indicates that the regional peer effect in enterprise ESG performance has a significantly positive effect on effectively enhancing a company’s green innovation capability and promoting corporate social responsibility. The research conclusions complement and enrich relevant findings in the field of corporate ESG behavior, providing theoretical and empirical evidence for central and local governments to formulate policies that effectively promote the improvement of enterprise ESG performance.