Paleohydrological data comprising pollen assemblages and leaf‐wax hydrogen isotopes (δDwax) from paleolake sediments in the Qaidam Basin (China) provide evidence for a link between increased moisture availability on the Tibetan Plateau and global cooling during the Mid‐Pleistocene Transition. Notably, they document the persistence of humid and cold conditions during Marine Isotope Stages 24–22 (936–866 ka) suggesting that boundary conditions favorable for extended glaciation on the Tibetan Plateau first developed at ~900 ka. Our δDwax results indicate a strong influence of proximal (monsoonal) moisture sources during that glacial, in agreement with the intensification of the interhemispheric moisture transport resulting from Antarctic ice volume increase at ~900 ka. The consistency of our results with other marine and terrestrial climate data sets suggests that extended glaciation on the Tibetan Plateau may have initiated ~500 ka earlier than previously assumed, implying that midlatitude ice sheets actively contributed to global cooling during the Mid‐Pleistocene Transition. Plain Language Summary The Mid‐Pleistocene Transition (MPT) marks an intensification of global cooling associated with an expansion of Earth's ice sheets. The Tibetan Plateau—today the most extensively glaciated region outside the high latitudes—may have played a pivotal role in this process. However, because its glaciation history is yet poorly constrained, testing this hypothesis has remained difficult. Here we assess the climatic boundary conditions for glacier development on the Tibetan Plateau during the MPT using pollen and organic biomarker data from paleolake sediments (Qaidam Basin, China). Our results suggest a link between increased moisture availability on the Tibetan Plateau and global cooling during Marine Isotope Stages 24–22. We infer that favorable conditions for extended glaciation on the Tibetan Plateau first developed at ~900 ka, that is, ~500 ka earlier than previously assumed, suggesting that ice sheet formation on the Tibetan Plateau indeed played an active role in global cooling during the MPT. Key Points Link between increased moisture availability on the Tibetan Plateau and global cooling during Marine Isotope Stages 24‐22 Favorable conditions for extended glaciation on the Tibetan Plateau first developed at ~900 ka Ice sheet formation on the Tibetan Plateau played an active role in global cooling during the Mid‐Pleistocene Transition