The purpose of this study is manifold. Firstly, it determines the roles played by the legislature in performing its oversight function in Nigeria’s Fourth Republic, from 1999 to 2019. Secondly and is a related purpose, it demonstrates how this function (oversight) has helped in democratic consolidation. Thirdly, it identifies the challenges of legislative oversight, and lastly, it adumbrates the implications of these challenges to democratization in the Nigerian politics. The Institutional agency theory propounded by Barry Mitnick is adopted in this paper as a framework of analysis. Hence, the study, which is basically empirical, generated the data from face-to-face interview using purposive sampling and case study research design. In doing so, the paper opines that for oversight function to strengthen democracy in Nigeria, the legislature should be financially autonomous and otherwise. Moreover, the degree of separation of powers should be improved and both the legislature and its staff should be trained frequently. Similarly, the paper concludes that there is need for the research improvement in the Nigerian National Assembly.

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