Modern slavery is a persistent human tragedy and a growing organisational risk. The United Nations’ Sustainable Development Goals highlight the significance of governments in shaping firms’ sustainability agenda and combating modern slavery. However, little is known about the effects of the institutional environment on modern slavery risk. This study, therefore, investigates the crucial policy question of whether the quality of the institutional environment has any effect on modern slavery and whether sustainable human development reinforces this relationship. Using data from 167 countries, we find that institutional environment quality is negatively associated with the prevalence of and vulnerability to modern slavery, and positively associated with its modern slavery risk mitigation. Our results suggest that democratically elected governments operating in politically stable societies with higher quality of voice and accountability, higher levels of control of corruption, and stricter rule of law are more accountable and responsive to modern slavery risks. We also find that sustainable human development (HDI) has a moderating effect on the relationship between institutional environment quality and modern slavery, and this effect is mainly noticeable in low HDI countries. These results imply that governance reforms alone might not yield the desired effects for all countries and, hence, have significant implications for policymakers, companies, and societal stakeholders.