Ferroptosis is a form of cell death that has received considerable attention not only as a means to eradicate defined tumour entities but also because it provides unforeseen insights into the metabolic adaptation exploited by tumours to counteract phospholipid oxidation. Here, we identify a pro-ferroptotic activity of 7-dehydrocholesterol reductase (DHCR7) and an unexpected pro-survival function of its substrate, 7-dehydrocholesterol (7-DHC). Although previous studies suggested that high levels of 7-DHC are cytotoxic to developing neurons and favour lipid peroxidation, we now demonstrate that 7-DHC accumulation confers a robust pro-survival function in cancer cells. 7-DHC, due to its far superior reactivity towards peroxyl radicals, is shown here to effectively shield (phospho)lipids from autoxidation and subsequent fragmentation. We further demonstrate in a subset of ferroptosis-sensitive Burkitt lymphomas - where DHCR7 mutations have been reported - that the accumulation of 7-DHC is sufficient to suppress the basal sensitivity of cells toward ferroptosis, thereby translating into an unexpected growth advantage. Conclusively, our findings provide compelling evidence of a yet-unrecognised anti-ferroptotic activity of 7-DHC as a cell-intrinsic mechanism that could be exploited by cancer cells to escape ferroptosis.