Although hypoxia is detrimental to most cell types, it aids survival of progenitor cells and is associated with diseases like cancer and pulmonary hypertension in humans. Therefore, understanding the underlying mechanisms that promote survival of progenitor cells in hypoxia and then developing novel therapies to stop their growth in hypoxia-associated human diseases is important. Here we demonstrate that the proliferation and growth of human CD133⁺ progenitor cells, which contribute to tumorigenesis and the development of pulmonary hypertension, are increased when cultured under hypoxic conditions. Furthermore, glucose-6-phosphate dehydrogenase (G6PD) activity was increased threefold in hypoxic CD133⁺ cells. The increased G6PD activity was required for CD133⁺ cell proliferation, and their growth was arrested by G6PD inhibition or knockdown. G6PD activity upregulated expression of HIF1α, cyclin A, and phospho-histone H3, thereby promoting CD133⁺ cell dedifferentiation and self-renewal and altering cell cycle regulation. When CD133⁺ cells were cocultured across a porous membrane from pulmonary artery smooth muscle cells (PASMCs), G6PD-dependent H₂O₂ production and release by PASMCs recruited CD133⁺ cells to the membrane, where they attached and expressed smooth muscle markers (α-actin and SM22α). Inhibition of G6PD reduced smooth muscle marker expression in CD133⁺ cells under normoxia but not hypoxia. In vivo, CD133⁺ cells colocalized with G6PD⁺ cells in the perivascular region of lungs from rats with hypoxia-induced pulmonary hypertension. Finally, inhibition of G6PD by dehydroepiandrosterone in pulmonary arterial hypertensive rats nearly abolished CD133⁺ cell accumulation around pulmonary arteries and the formation of occlusive lesions. These observations suggest G6PD plays a key role in increasing hypoxia-induced CD133⁺ cell survival in hypertensive lungs that differentiate to smooth muscle cells and contribute to pulmonary arterial remodeling during development of pulmonary hypertension.