Continental scale ice sheets have occupied Antarctica since the major global cooling across the Eocene/Oligocene boundary (~33.9 Ma). However, the timing and nature of the transition to a relatively stable and persistent terrestrial East Antarctic Ice Sheet that characterizes the modern environment remains disputed. Although proxy data show global surface temperatures remained significantly warmer through the late Miocene than today, the hypothesis that the upper elevations of the McMurdo Dry Valleys remained under a hyper-arid polar climate since the mid-Miocene has persisted. Here, we constrain the onset of polar aridity in the McMurdo Dry Valleys region using meteoric Beryllium-10 as a tracer of water infiltration in mid-Miocene and late Quaternary-age soils at three sites situated >1000 m a.s.l.. Our results show that meteoric Beryllium-10 infiltrated the soils for a period after sediment emplacement ~15.0 – 14.0 Ma, terminating at ~6.0 Ma. Reconstruction of climate from paleo-active layer thickness and threshold of mobility of meteoric Beryllium-10 suggests that at 6.0 Ma, summer temperatures were 7 – 10°C with annual precipitation >10 mm. Polar aridity at high elevations has persisted since ~6.0 Ma, well after previous reconstructions (13.8 – 12.5 Ma). Together, our findings indicate that high elevations of the McMurdo Dry Valleys experienced interval(s) of warm-wet climate between ~14.0 – 6.0 Ma which reconciles observations of coastal warmth and reduced ice in the Ross Embayment.