Characterized by low temperatures, low oxygen availability and strong ultraviolet radiation, the Third Pole glacier region is highly sensitive to global change. Despite overall vegetation recovery, succession accelerated by rapid glacier ablation poses unknown risks. We integrated multitemporal records for 36,374 glaciers with remote-sensing, reanalysis and environmental datasets to assess forefield vegetation dynamics and their climatic, edaphic and topographic controls. Our results showed that glacier forefields covered 7003.11 km², and were concentrated at elevations of  4000–6000 m. From the earliest recorded glacier outlines to 2022, mean retreat area per glacier was clearly greater in the monsoon region than in the westerly region (0.389 versus 0.122 km²). Across these forefields, the normalized difference vegetation index (NDVI) increased significantly from 2000 to 2022 (slope = 0.013 decade⁻¹, R² = 0.607, p < 0.001). Both greening and growing-season lengthening were significantly faster in the monsoon region than in the westerly region (0.018 versus 0.009 decade⁻¹ and 3.80 versus 0.20 days decade⁻¹, respectively; p < 0.001). Our results also revealed that NDVI was associated with thermal conditions and soil properties, including field capacity, soil organic carbon and bulk density. Overall, vegetation succession in Third Pole glacier forefields is a staged process triggered by climate warming and snow-cover change, progressively supported by soil development and constrained over the long term by high-elevation terrain. Together, these findings reveal spatially uneven greening trajectories across Third Pole glacier forefields and suggest that their environmental constraints change as newly exposed landscapes develop, providing a scientific basis for understanding alpine ecosystem responses to climate change in extreme habitats.