Do global value chains (GVCs) make firms cleaner, and under what conditions? Leveraging rich firm-level data from India in the period of 2010–2024, this study investigates the impact of GVC participation on firms’ environmental performance. To address dynamics and heterogeneous responses, we estimate dynamic panel threshold regressions with firm growth as the regime variable. We find that GVC participation raises energy and carbon intensity for low-growth firms but reduces both—and increases renewable energy use—for high-growth firms. Channel decomposition shows that forward participation delivers the clearest efficiency and decarbonization gains in the high-growth regime, while backward participation improves energy efficiency at high growth yet exhibits mixed carbon effects; in the low-growth regime, forward linkages raise intensity whereas backward linkages are comparatively less harmful or even carbon-reducing. This paper underscores the capacity-dependence of trade integration’s environmental impact and shows that policy can shift the relevant margin through finance, R&D, and compliance infrastructure.