Developing a Theory of Islamic Constitutionalism for Multi-Religious Federal States: Lessons from Nigeria’s Sharia Experience

Islamic constitutionalism, the theoretical framework for organising state structures in accordance with Islamic political and legal principles within a constitutional order, has been theorised primarily in the context of Muslim-majority unitary states. Its application to genuinely multi-religious federal states, where Islamic law operates as one component of a pluralistic legal order, requires original theoretical development drawing on Nigeria's twenty-five-year experience as a case study. This study develops an original theory of Islamic constitutionalism for multi-religious federal states, drawing on the Nigerian Sharia experience from 1999 to 2024. The theoretical development employs a three-source methodology: systematic analysis of classical Islamic political jurisprudence (Fiqh al-Siyasa), comparative constitutional law theory of federal systems with religious diversity, and empirical institutional analysis of Nigeria's Sharia state arrangements. The empirical component reviews constitutional amendment proposals, court decisions on Sharia jurisdiction, and structured interviews with thirty Islamic constitutional scholars and political actors. The study critically engages with existing Islamic constitutionalism theories from Khaled Abou El Fadl, Abdullahi an-Na'im, and Mohammad Hashim Kamali, identifying their limitations for plural federal contexts. The original theoretical contribution is a Federal Islamic Constitutional Model proposing five principles for sustainable Islamic law application in multi-religious federal states: jurisdictional voluntarism, rights floor protection, structural Shura, minority protection obligations, and evolutionary Ijtihad institutions. Keywords: Islamic constitutionalism, federal state, Nigeria, political jurisprudence, religious pluralism.