This study attempted to examine the long-run relationship and direction of causality between economic growth and government spending with consideration for exchange rate, consumer prices and monetary policy rate. This is with a view to determine the validity of Wagner’s law in Nigeria during the period 1961 to 2011. Times series data on variables such as real GDP, government expenditure, exchange rate, inflation rate and monetary policy rate during the period (1961-2011) were used. These data were sourced from Central Bank of Nigeria (CBN) Statistical Bulletin 2011 Edition; World Development Indicator (WDI) Latest version and Federal Ministry of Finance. The study identified the order of integration of the variables used in the study using Phillips-Perron unit root test. The test was conducted with a drift and Time trend. The study also employed Johansen multivariate cointegration tests to determine if a group of I(1) variables converge to a long-run equilibrium. Vector Error Correction Mechanism was employed to model causal relation between economic growth and government spending. The results showed that variables are individually integrated of order one that is, a I(1) process. Johansen multivariate cointegration test showed that variables are cointegrated. Both the Trace test and Maximum-Eigen test suggest one cointegrating vector. The result of VECM estimates provided evidence in support of long-run causality running from real GDP to government spending. However, while evidence exists for long-run causality running from real GDP to government spending such evidence does not exist for short-run causality in this same direction. This indicates that Wagner’s Law is supported only in the long-run. The study therefore concludes that Wagner’s law is never a Myth but a Reality in Nigeria over the sample period.