This study investigates the long-run and short-run relationships among insecurity, poverty, human capital development, and sustainable economic development in Nigeria from 2000 to 2023. Drawing on the multidimensional poverty and education frameworks of researchers, the study employs annual time-series data from the World Development Indicators, Central Bank of Nigeria, and National Bureau of Statistics. Using Augmented Dickey-Fuller unit root tests, Johansen cointegration analysis, and Autoregressive Distributed Lag (ARDL) bounds testing, the study examines the dynamic interrelationships among Adjusted Net Savings (ADJNS- proxy for sustainable development), defence expenditure (proxy for insecurity), poverty rate, life expectancy, per capita income, and secondary school enrollment (proxy for human capital development). The ARDL bounds test confirms a significant long-run cointegrating relationship among the variables. Findings reveal that in the long run, human capital development (school enrollment) exerts the largest positive influence on sustainable development, followed by per capita income and defence expenditure. Conversely, poverty rate and life expectancy exhibit negative long-run effects. The error correction indicates rapid adjustment to equilibrium following short-term shocks. The study concludes that human capital development mediates the poverty-sustainability relationship, with indirect effects through education exceeding direct poverty effects. Policy recommendations include prioritising education investment, implementing integrated poverty reduction strategies that address both income and capability deprivations and strengthening social security frameworks to transform demographic gains into sustainable development outcomes.