This article investigates the dynamic relationship among competition, diversification and bank performance using data for 18 countries with a dual banking system over the period 2000 to 2016. Analyses using panel vector autoregression (PVAR) model, impulse response function (IRF) and variance decomposition (VDC) methods confirm that market power increases the profitability and the stability of banks the dual banking system while revenue diversification reduces them. Market power increases revenue diversification of banks. Segregating the sample of banks into emerging and developing countries, we find that positive impact of market power on profitability is stronger for emerging countries. Even though we find that revenue diversification has a more damaging effect on the profitability of banks in the developing countries, it only dampens the stability of banks in emerging countries. In addition, we find that asset diversification dampens the stability of banks. However, it has a more positive impact on the profitability of banks in emerging economies.