This study examined the effect of corporate governance mechanisms on the financial performance of listed Deposit Money Banks (DMBs) in Nigeria. Specifically, the study investigated the effect of board size, board gender diversity, board independence, board meeting frequency, and audit committee size on financial performance, return on assets (ROA). The study adopted an ex-post facto research design, with data extracted from the published audited annual financial reports of 16 listed Deposit Money Banks in Nigeria over a ten-year period (2015–2024). The data collected were subjected to diagnostic tests including correlation analysis, variance inflation factor, and normality tests to ensure validity and reliability. Panel data analysis was employed, and multiple regression analysis was conducted, with the Ordinary Least Squares (OLS) model found most appropriate for hypothesis testing. The findings revealed that board size has a significant positive effect on financial performance; board gender diversity has an insignificant effect; board independence significantly enhances financial performance; board meeting frequency significantly improves performance; and audit committee size also exerts a positive and significant effect on the financial performance of listed Deposit Money Banks in Nigeria. Based on these findings, the study recommends that Deposit Money Banks strengthen their governance structures by appointing directors with diverse experience, financial literacy, and professional expertise to the board and audit committees, as this will enhance sound decision-making and sustainable financial performance.