This research examined the challenges and opportunities associated with enhancing transparency and accountability in revenue mobilization within Nigeria’s public financial management (PFM) system. The study interrogates why Nigeria continues to experience persistent revenue underperformance despite ongoing institutional and policy reforms. Drawing on theoretical insights from Principal–Agent Theory and Public Choice Theory, the research adopts a qualitative analytical approach grounded in secondary data from government reports, international financial institutions, and empirical studies. Findings revealed that although Nigeria has recorded significant improvements in revenue collection, particularly through digitalization initiatives and reforms such as the Treasury Single Account and the Petroleum Industry Act, systemic challenges continue to undermine transparency and accountability. Key constraints such as institutional fragmentation, weak data management systems, corruption, political interference, high cost of revenue collection, and the predominance of the informal sector, contributes to revenue leakages, limited fiscal space, and weakened public trust in government institutions. The study also identified emerging opportunities for reform, including the expansion of digital tax systems, adoption of Integrated Financial Management Information Systems, implementation of international accounting standards, and increased civic engagement in fiscal governance. It argued that strengthening transparency and accountability requires not only technical reforms but also institutional realignment, improved oversight mechanisms, and enhanced political commitment. The paper concludes that sustainable improvement in Nigeria’s revenue mobilization depends on integrated reforms that address governance deficits, broaden the tax base, reduce collection inefficiencies, and reinforce the fiscal social contract. These measures are essential for promoting efficient resource utilization, reducing dependence on borrowing, and achieving long-term national development.