Purpose: This paper aims to investigate the nonlinear relationship between government debt and economic growth in Vietnam, specifically identifying the threshold levels at which the impact of debt shifts from positive to negative. Design/methodology/approach: A threshold regression model is employed to analyze the marginal impact of Vietnam's government external debt on GDP growth. The model incorporates various control variables, including total factor productivity, foreign direct investment, private debt, and trade openness. Findings: This research distinguishes itself by focusing on Vietnam's specific context to identify and quantify a precise, non-linear external debt threshold using a threshold regression model, moving beyond general linear assumptions. It provides a quantifiable estimate of debt's impact on growth across varying levels: 36,61% and 78,94%. Moreover, emphasizing the role of moderating factors like productivity, private debt, and trade openness, this research suggests the optimal threshold of public debt-to-GDP ratio for Vietnam is 36.16% represents a critical threshold. Below this level, government debt positively impacts economic growth. However, exceeding this threshold can lead to negative consequences, as total factor productivity and private debt may hinder growth.