This study draws on agenda-setting and legitimacy theories to examine whether negative ESG-related media coverage influences firms’ adoption of voluntary carbon assurance. Using a panel of U.S. firms from 2012 to 2020, we find that firms facing higher ESG reputation risk are more likely to engage in carbon assurance as a strategic response to stakeholder scrutiny and legitimacy threats. This effect is stronger among firms with higher institutional ownership, greater analyst coverage, elevated political risk, and Big Four auditors, contexts that heighten external accountability. These findings are robust to alternative measures, model specifications, and endogeneity checks. Conversely, the relationship is weaker among carbon-intensive firms and those with stronger environmental performance, suggesting variation in assurance strategies. Exploiting the U.S. withdrawal from the Paris Agreement as a quasi-natural experiment, we show that firms with high ESG risk significantly increased assurance uptake in the post-announcement period. Overall, our findings identify media-driven reputation risk as a distinct and underexplored driver of carbon assurance, with practical implications for regulators, investors, and standard-setters.