Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, characterized by profound heterogeneity and a dismal prognosis with a median overall survival rate of 15 months after diagnosis. The current standard-of-care is maximally safe surgical resection, followed by radiation and temozolomide. Recurrence is inevitable, after which survival rates drop to just 5 months. A key driver of GBM aggressiveness is the subpopulation of glioma stem cells (GSCs) which exhibit enhanced self-renewal, multipotency, and therapeutic resistance. The RNA binding protein, Muscleblind-like 1 (MBNL1), is responsible for stem cell maintenance and differentiation. MBNL1 is inactivated in GSCs, specifically under hypoxic conditions. Hypoxia, a hallmark of the GBM microenvironment, is a major regulator of GSC maintenance and tumor progression. We show that MBNL1 directly binds to the 3' untranslated region (3'UTR) of hypoxia inducible factor-1 alpha (HIF-1α) mRNA, promoting its degradation and suppressing the hypoxic transcriptional program. Loss of MBNL1 leads to increased HIF-1α mRNA stability, heightened expression of HIF-1 target genes, and enhanced stemness, proliferation, and clonogenicity of GSCs. Furthermore, MBNL1 regulates the duration of the hypoxic response, effectively limiting hypoxia memory and promoting cellular homeostasis upon reoxygenation. These findings position the MBNL1-HIF-1α axis as a promising therapeutic target for GBM, warranting further investigation to translate these discoveries into clinical applications.