This study explores the underlying drivers of the tone of corporate social responsibility (CSR) narratives by considering four corporate governance mechanisms and examining whether there is a relationship between environmental, social, and governance (ESG) disclosure and the CSR narrative tone based on a sample of UK firms from 2008 to 2017. The results show that more independent directors would lead to a less optimistic language (positive tone) and a more pessimistic language (negative tone) in the CSR report. The results also show that a higher ESG disclosure score leads to a more positive CSR narrative tone. However, gender diversity has a positive impact on the positivity of CSR tone when the ESG score is medium or high and when the board size exceeds 10 members. These findings are relevant for policymakers, investors, and firm managers. For instance, the findings inform regulators and policymakers about the relevant governance mechanisms that affect the tone of CSR reports.