This study examines the impact of public debt sustainability on the economic growth of Nigeria over a 39-year period, 1985 to 2024. The analysis focuses on three key sustainability indicators, the debt-to-GDP ratio, the interest–growth differential, and the external debt-to-export ratio, with real GDP employed as a proxy for economic growth. Time-series data obtained from the Central Bank of Nigeria, the Debt Management Office, and international financial databases are estimated using the Autoregressive Distributed Lag (ARDL) model to identify both short-run and long-run effects. The findings indicate the presence of a long-run equilibrium relationship among the variables. The debt-to-GDP ratio has a positive and significant impact on economic growth in the short run, but its long-run impact is minimal. The interest–growth differential exerts a significant negative effect on growth in the short run, reflecting the strain of rising borrowing costs on economic performance. Similarly, the external debt-to-export ratio has a significant negative short-run impact, indicating vulnerability to external repayment pressure. The study concludes that debt sustainability is a crucial factor in determining Nigeria’s economic performance and recommends that government manage public debt prudently, allocate borrowed resources productively, and pursue policies that sustain a favourable macroeconomic environment.

Keywords: Public Debt, Debt-to-GDP Ratio, Interest–Growth Differential, External Debt-to-Export Ratio, Economic Growth.