This study examines the impact of public expenditure on human capital development (HCD) in Nigeria over the period 1960 to 2024, incorporating five categories of control variables: demographic factors (DF), macroeconomic factors (MF), institutional factors (INSF), global factors (GF), and infrastructural factors (INFF). Using a cross-sectional time-series regression framework — including Ordinary Least Squares (OLS), Fixed Effects (FE), and Random Effects (RE) panel models — and the Human Development Index (HDI) as the primary proxy for HCD, the study finds that public expenditure on education, health, and social protection each exerts a statistically significant and positive effect on human capital development in Nigeria. The results are robust to the inclusion of all control variables. Among the control variables, infrastructure quality, governance quality, and GDP per capita emerge as the most influential determinants of HCD, while high inflation and rapid population growth exert significant negative effects. The Hausman test confirms the appropriateness of the Random Effects estimator for the full model. Post-estimation diagnostics confirm the absence of heteroskedasticity, serial autocorrelation, and functional misspecification. The study reveals that the persistent underperformance of Nigeria's human capital relative to its peers is attributable not just to the quantity but to the quality and efficiency of public spending. The findings carry significant policy implications for sub-Saharan Africa's most populous economy and contribute to the growing body of evidence on public finance and development outcomes in emerging markets.