Endoplasmic reticulum (ER) stress and major chemotherapeutic agents invariably trigger oxidative stress, but the exact mechanism was not known. We found that ER stress and major chemotherapeutic agents induce leukotriene C4 (LTC4) biosynthesis in cells of non-hematopoietic lineage by assembly on the nuclear envelope of an LTC4 biosynthetic machinery based on microsomal glutathione-S-transferase 2 (MGST2). ER stress and chemotherapy also triggered nuclear translocation of the two LTC4 receptors. Acting in an intracrine manner, LTC4 then elicits nuclear translocation of NADPH oxidase 4 (NOX4), resulting in accumulation of reactive oxygen species (ROS) and subsequent DNA damage. Mgst2 deficiency, RNAi and LTC4 receptor antagonists abolished ER stress- and chemotherapy-induced oxidative nuclear DNA damage and dsDNA breaks in vitro and in mouse kidneys. Cell death and mouse morbidity were also significantly attenuated. Hence, MGST2-generated LTC4 is a major mediator of ER stress- and chemotherapy-triggered oxidative stress, leading to oxidative DNA damage and dsDNA breaks. Previous studies demonstrated that LTC4 inhibitors, commonly used as approved asthma drugs, attenuated neurological damage, cardiovascular damage and drug toxicity. Our findings provide the mechanism by which these pathophysiological conditions lead to cellular damage, suggesting a broad use of LTC4 inhibitors in major human morbidities.