This study examines the impact of financial deepening on economic growth in Nigeria over the period 1986-2017. Data for the study were obtained from secondary sources (Central Bank of Nigeria Statistical Bulletin). The explanatory variables used are ratio of broad money supply to GDP (MSGP) and ratio of private sector credit to GDP (CPGD). The study was carried out using Ordinary Least Square, Augmented Dickey Fuller unit root test, the Johansen approach to co-integration analysis and granger causality approach. This study found that money supply has a positive and insignificant impact on the economic growth. The past credit to private sector to gross domestic product at lags 1 has a negative and significant impact on the economic growth in Nigeria. There is uni-directional causal relationship running from ratio of money supply to economic growth. However, the result of granger causality test revealed that ratio of broad money supply to gross domestic product and ratio of private sector credit to gross domestic product has bi-directional causal relationship with economic growth. The results highlight the importance of the Nigerian financial intermediary sector in resource mobilization and allocation and in stimulating economic activities. The development of financial sector intermediation could therefore be the right strategy lessening the dominance of the oil sector in the Nigerian economy. The Financial system reforms should be continued to ensure efficient allocation of resources and management of money supplied in the economy. Conclusively, the results show that financial deepening has significant impact on economic growth, therefore, the assertion is that financial deepening drives economic growth. The study recommended that part of government resources should be spent towards the reduction of risks which inhibits investments in Nigeria. These include provision of adequate security to stem increasing kidnapping, assassination and terrorism as well as the provision of inadequate public power supply and efficient transportation infrastructure. These will boost and enhance the establishment of new investments as well as expansion and efficiency of the old ones. Keyword: Financial deepening, Economic Growth, Broad money supply, Bank credit to private sector, co-integration.