["Corporate Social Responsibility and Environmental Management, EarlyView. ", "\nABSTRACT\nAs regulatory and stakeholder pressures intensify, firms are increasingly expected to move beyond symbolic sustainability commitments towards corporate climate activism. This concept refers to the active institutionalisation of climate‐focused mechanisms such as external assurance, board oversight and climate‐linked incentives. Given that female directors are often associated with enhanced monitoring and greater sensitivity to long‐term stakeholder risks, this study posits that gender diversity is a crucial driver of these substantive board‐level refinements. This study investigates the impact of board gender diversity on corporate climate activism among non‐financial firms in the S&P 500 index. Using a panel of 4376 firm‐year observations, we investigate whether and how gender diversity at the board level influences carbon‐sensitive firms' climate activism. Our findings show that greater gender diversity on boards drives firms' climate‐focused efforts. The positive association holds when we use alternative measures such as the Blau index and the absolute number of female directors. Further analysis suggests that the presence of two or more women on corporate boards is necessary for women to exert a significant impact on climate activism, consistent with critical mass theory. These results remain robust across instrumental variable estimation, propensity score matching and the Heckman selection model. Our study contributes to the related literature by providing empirical evidence that gender diversity plays a pivotal role in shaping firms' climate‐responsible strategies and climate risk management.\n"]