The principle of amānah (trusteeship) in Islamic jurisprudence transcends personal morality, functioning instead as a foundational norm for legitimizing the state’s control over public assets. Understood as a divine mandate of fiduciary responsibility, this principle delineates the boundaries of state authority and offers a conceptual anchor for institutional transparency, accountability, and intergenerational justice. This study adopts a comparative-analytical approach to examine the application of this principle in two distinct Islamic legal systems: Iran’s National Development Fund, established under Article 45 of the Constitution with a wilāyat al-faqīh–based interpretation of trusteeship; and the United Arab Emirates’ Abu Dhabi Investment Authority (ADIA), a sovereign wealth fund operating within the framework of an accountable federal monarchy and a vision of strategic generational equity. Through a comparative analysis of legal structures, legitimacy doctrines, oversight institutions, and financial governance mechanisms, the article demonstrates that, while both systems claim a trust-based model for managing public wealth, their divergent theological and political foundations have produced two distinct models of state–citizen–future relations. The findings suggest that a renewed engagement with the Islamic notion of trusteeship can inform the reconfiguration of state financial institutions toward greater accountability, transparency, and legitimacy within Islamic public law.