This study examines whether national secrecy culture influences firms’ supply chain disclosure transparency in the global fashion industry. Using a sample of 545 firm-year observations from leading global fashion brands and retailers across 21 countries from 2015 to 2022, we measure supply chain disclosure transparency with the Fashion Transparency Index and proxy for country-level secrecy culture with established Hofstede-based cultural measures. We document a positive, statistically significant association between a secrecy culture and supply chain disclosure transparency. Further analyses reveal that this relationship is weaker in stakeholder-oriented and strong-governance countries, but stronger in financially opaque environments, highlighting the moderating role of formal institutional contexts. These findings challenge the conventional view that secrecy-oriented cultures uniformly discourage transparency and instead provide evidence of a compensatory disclosure mechanism in voluntary non-financial reporting. By extending the secrecy culture literature beyond financial reporting to supply chain transparency, this study advances understanding of how informal institutions shape corporate disclosure strategies in sustainability-sensitive global industries. Our findings have important implications for regulators, investors, and managers seeking to enhance accountability and transparency in complex global supply chains.