The value of informatization lies not only in expanding urban digital infrastructure, but also in reshaping firm behavior through improvements in the information environment. Using China’s smart city pilot program as a quasi-natural experiment and a sample of Chinese A-share listed firms, this study examines whether urban-level informatization affects corporate ESG performance. The staggered difference-in-differences estimates show that smart city pilots significantly improve firms’ ESG performance, and the result remains robust after a range of endogeneity checks and robustness tests. Mechanism analyses provide evidence consistent with the proposed external monitoring and internal governance channels. Specifically, smart city pilots are associated with stronger monitoring by capital-market participants and improved internal governance conditions, in line with investor attention theory and organizational information processing theory. The effect is more pronounced for firms whose executives have environmental backgrounds, firms in heavily polluting industries, and firms located in regions with stronger environmental regulation. Further tests show that ESG improvements induced by informatization increase both short-term profitability and long-term market valuation. These findings reveal how urban informatization promotes corporate ESG performance and show that ESG improvements can help firms align social value with economic value.