Glioblastoma (GBM) employs various strategies to resist therapy, resulting in poor patient survival. A key aspect of its survival mechanisms lies in metabolic regulation, maintaining rapid growth and evading cell death. Recent studies revealed the connection between therapy resistance and ferroptosis, a lipid peroxidation-dependent cell death mechanism triggered by metabolic dysfunction. Our aim was to identify novel regulators of therapy resistance in GBM cells. We conducted a comprehensive analysis combining RNA-sequencing data from a panel of human GBM cell models and TCGA GBM patient datasets. We focused on the top-12 differentially expressed gene candidates associated with poor survival in GBM patients and performed an RNA interference-mediated screen to uncover the radiochemosensitizing potential of these molecules and their impact on metabolic activity, DNA damage, autophagy, and apoptosis. We identified exostosin glycosyltransferase 2 (EXT2), an enzyme previously described in heparan sulfate biosynthesis, as the most promising candidate. EXT2 depletion elicited reduced cell viability and proliferation as well as radiochemosensitization in various GBM cell models. Mechanistically, we explored EXT2 function by conducting untargeted and targeted metabolomics and detected that EXT2-depleted GBM cells exhibit a differential abundance of metabolites belonging to S-adenosylmethionine (SAM) metabolism. Considering these metabolic changes, we determined lipid peroxidation and found that the diminished antioxidant capacity resulting from decreased levels of metabolites in the transsulfuration pathway induces ferroptosis. Moreover, modifications of specific SAM and transsulfuration metabolism associated enzymes revealed a prosurvival and ferroptosis-reducing function when EXT2 is depleted. Collectively, our results uncover a novel role of EXT2 in GBM cell survival and response to X-ray radiation, which is controlled by modulation of ferroptosis. These findings expand our understanding of how GBM cells respond to radio(chemo)therapy and may contribute to the development of new therapeutic approaches.