This paper aimed to determine the significance of foreign direct investment inflow on economic growth in Nigeria using financial development as a control variable, and ascertain the causal relationship among foreign direct investment inflow, financial development and economic growth. Study's data is the Nigeria economic data from 1982 to 2014 obtained from the central bank of Nigeria statistical bulletin. The ordinary least square method of estimating multiple regression was employed to regress economic growth on foreign direct investment inflow, financial development, exports and labour and the t statistics to test the study's hypotheses at 5% level of significance, the augmented Dickey fuller Unit root test and Granger causality test were also used. Results established a unidirectional causality flowing from financial development to gross domestic product growth. The individual effects of financial development or foreign direct investment are negative, however this negative relationship turned positive when their joint effect is considered as established by the positive and significant coefficient of the interaction variable between foreign direct Investment inflow and financial development, thus the significance and positive coefficient of foreign direct investment in effecting the desired growth in output is subject to financial development. The government should encourage foreign direct investment inflows through infrastructural development, political stability, tax and other fiscal incentives, however these should be complimented with policies that foster financial development