The study determines the impact of corporate governance mechanisms on the performances of banks in Nigeria, with a focus on emerging economy dynamics. Using data from listed Nigerian banks, performance was measured by return on assets (ROA), return on equity (ROE), Tobin’s Q, and non-performing loans (NPLs). Governance variables included size of board, independence of board, duality of CEO, independence of audit committee, and ownership concentration, while bank-specific and macroeconomic factors were controlled for. The study findings reveal that the size of board positively influences profitability, supporting the roles of monitoring and resource provision of larger boards. Board independence, however, shows no significant effect, reflecting institutional weaknesses where “independent” directors often lack autonomy. CEO duality negatively impacts performance and increases NPLs, consistent with agency theory concerns about power concentration. Audit committee independence strongly enhances profitability and reduces credit risk, underscoring the importance of effective oversight. Conversely, ownership concentration reduces profitability and increases NPLs, suggesting entrenchment effects in Nigeria’s banking sector. Control variables behave as expected: larger banks perform better, while higher leverage and inflation raise risks. These results provide new insights into the governance–performance nexus in an emerging economy context, highlighting both the relevance of traditional governance mechanisms and the constraints imposed by weak institutional environments. The study recommends strengthening regulatory enforcement, enhancing board diversity, limiting CEO duality, and addressing ownership entrenchment to improve governance effectiveness in Nigerian banks.