The environmental implications of corporate economic activities have led to growing demands for firms and their boards to adopt sustainable strategies and to disseminate more useful information about their activities and impacts on environment. This paper investigates the impact of board's corporate social responsibility (CSR) strategy and orientation on the quantity and quality of environmental sustainability disclosure in UK listed firms. We find that effective board CSR strategy and CSR‐oriented directors have a positive and significant impact on the quality of environmental sustainability disclosure, but not on the quantity. Our findings also suggest that the existence of a CSR committee and issuance of a stand‐alone CSR report are positively and significantly related to environmental sustainability disclosure. When we distinguish between firms with high and low environmental risk, we find that the board CSR/sustainability practices that affect the quantity (quality) of environmental sustainability disclosure appear to be driven more by highly (lowly) environmentally sensitive firms. These results suggest that the board CSR/sustainability practices play an important role in ensuring a firm's legitimacy and accountability towards stakeholders. Our findings shed new light on this under‐researched area and could be of interest to companies, policy‐makers and other stakeholders. Copyright © 2017 John Wiley & Sons, Ltd and ERP Environment