The study reveals that inositol-requiring enzyme 1 (IRE1α), an endoplasmic reticulum (ER) resident protein, plays a critical role in determining cellular sensitivity to ferroptosis. IRE1α depletion in both cancer and normal cells increases resistance to ferroptosis, while enhanced IRE1α expression promotes sensitivity. Mechanistically, IRE1α's endoribonuclease activity cleaves and down-regulates the mRNA of key glutathione biosynthesis regulators, glutamate-cysteine ligase catalytic subunit (GCLC) and solute carrier family 7 member 11 (SLC7A11). This activity is independent of its role in the unfolded protein response (UPR) and is evolutionarily conserved. Genetic deficiency and pharmacological inhibition of IRE1α reduce ferroptosis and renal ischemia-reperfusion injury in mice. The findings suggest that inhibiting IRE1α could be a promising therapeutic strategy to mitigate ferroptosis-associated pathological conditions.The study reveals that inositol-requiring enzyme 1 (IRE1α), an endoplasmic reticulum (ER) resident protein, plays a critical role in determining cellular sensitivity to ferroptosis. IRE1α depletion in both cancer and normal cells increases resistance to ferroptosis, while enhanced IRE1α expression promotes sensitivity. Mechanistically, IRE1α's endoribonuclease activity cleaves and down-regulates the mRNA of key glutathione biosynthesis regulators, glutamate-cysteine ligase catalytic subunit (GCLC) and solute carrier family 7 member 11 (SLC7A11). This activity is independent of its role in the unfolded protein response (UPR) and is evolutionarily conserved. Genetic deficiency and pharmacological inhibition of IRE1α reduce ferroptosis and renal ischemia-reperfusion injury in mice. The findings suggest that inhibiting IRE1α could be a promising therapeutic strategy to mitigate ferroptosis-associated pathological conditions.