We analyze how transitioning to low-carbon energy sources affects sovereign debt sustainability through a data-driven, integrated modeling framework that combines climate change assessment models with stochastic debt sustainability optimization. Using scenarios from the Network for Greening the Financial System (NGFS), we evaluate orderly and disorderly transitions aligned with the Paris Agreement target of limiting global warming below 2°C. Our analysis quantifies both the transition risk premium affecting debt financing costs and the impacts on economic growth, influencing the debt-to-GDP ratio. We find significant increases in sovereign debt for fifteen countries worldwide, starting in the late 2030s. To offset these debt increases, annual fiscal adjustments averaging up to 1.1% of GDP would be necessary, with substantial cross-country differences. Stabilizing heightened debt levels due to the energy transition would require total fiscal adjustments averaging between 1.2% and 1.4% of GDP, depending on climate projections. Additionally, transition risks incentivize debt management toward longer maturities. Achieving green growth of approximately 0.5% from the transition could offset these debt impacts. Recycling carbon tax revenues toward debt repayment could also improve debt sustainability under some conditions.