The study interrogated the nexus between reforms in internal revenue generation and the fiscal viability of Lagos State, Nigeria. The article adopted the theory of fiscal federalism arguing that the reforms initiated by Lagos State Government in internal revenue generation largely accounted for the fiscal viability of the state in Nigeria. These reforms were targeted at harnessing and increasing internal revenue accruable to the State. Documentary method and content analysis were adopted for data collection and analysis. Findings indicate that the reforms increased Lagos State IGR from N201.76bn in 2011 to N301.19bn in 2018. This represented about 1,232.35, accounting for over 68.31 percent of the state annual budget between 2010 and 2018.  The viability of the state was demonstrated in her ambitious and aggressive infrastructural development and her unique budget size, on the basis of which the state was able to surmount other challenges like provision of basic services and payment of emoluments of workers and pensioners in the state. Drawing from the findings above, the study recommends sustenance of the present tempo in internal revenue drive by blocking all leakages, regular stakeholders’ engagement, review and update of revenue data, as a basis of revenue projections and transparency in the utilization of generated revenue.