The liquidity of stock markets in emerging economies remains a critical determinant of capital formation and economic stability. In Nigeria, the Nigerian Exchange Group (NGX) has historically grappled with liquidity constraints, often attributed to information asymmetry and weak corporate governance. This study investigates the impact of institutional ownership on the stock market liquidity of listed firms in Nigeria, utilizing a comprehensive dataset of 151 non-financial and financial firms over the period 2011 to 2025. Employing an ex-post facto research design and panel regression techniques, the analysis incorporates control variables including firm size, industry type, leverage, profitability, and growth opportunities. The findings reveal a statistically significant positive relationship between institutional ownership and stock market liquidity, suggesting that institutional investors act as monitors who reduce information asymmetry and enhance trading activity. Conversely, high leverage and concentrated industry competition were found to dampen liquidity. The study contributes to the literature by providing updated empirical evidence post-2016 economic recession and offers actionable recommendations for the Securities and Exchange Commission (SEC) and corporate managers to foster a more liquid investment climate.