The environmental, social, and governance index has seen significant growth in recent times as a representative of responsibility, transparency, and social accountability with its impact evident in the firm's stock price (Engelhardt et al., 2021). This event study investigates the influence of the inclusion of Indian firms into the Environment, Social, and Governance Index (BSE, ESG index) on their stock market performance. A total of 200 firms form the basis of the investigation for the study including firms from the BSE ESG index to form the sample group and another group, based on market capitalization, asset size, and industry type as the control group. The study uses an independent sample t-test to evaluate the difference in the stock market performance of the sample and control group, on a daily basis (+10), weekly basis (+10), monthly basis (+9), and quarterly basis (+4), post inclusion in ESG index. The results suggest a substantial difference in the stock market performance of the sample and control group post-announcement. The difference diminishes as we go farther from the announcement date of inclusion in the case of weekly and quarterly comparisons. The inferences from the binary logistic regression model also suggest that a significant positive effect of ESG index inclusion was found on the stock market performance of the firm on a daily and weekly basis which is not true for monthly and quarterly basis. This implies a notable and immediate change in stock market performance due to the inclusion of the ESG index on a daily and weekly basis. However, this effect is not observed over the intermediate term, specifically on a monthly and quarterly basis. The results are in concurrence with the existing research suggesting that inclusion in the ESG index, projects a company as better performing, enhances its reputation, leads to good word of mouth, and hence reflects in the stock price of the firm (Sahut and Pasquini-Descomps, 2015; Shanaev and Ghimire, 2022).