This study examines the legal implications of federalism on the security architecture of Nigeria, focusing on the constitutional concentration of security powers in the federal government and its consequences for effective security governance. Although Nigeria operates a federal system of government consisting of thirty-six states and the Federal Capital Territory, the Constitution of the Federal Republic of Nigeria 1999 (as amended) centralises the control of the armed forces and the police under the federal government. This structural arrangement has generated significant legal and institutional challenges, particularly in the management of rising security threats such as: insurgency, banditry, communal violence, and organised crime. Using the doctrinal research methodology, the paper examined the relevant constitutional provisions, statutory frameworks, and judicial decisions regulating the appointment of heads of security agencies and the allocation of security powers within Nigeria’s federal structure. The study finds that the existing centralised security framework undermines the principles of federalism and limits the ability of state governments to respond effectively to local security challenges. It argues that meaningful reform of Nigeria’s security governance requires constitutional restructuring that decentralises policing responsibilities while maintaining coordinated national oversight. The paper recommends the establishment of state police and strengthened accountability mechanisms in the appointment and oversight of security leadership