Acquired drug resistance prevents cancer therapies from achieving stable and complete responses. 1 Emerging evidence implicates a key role for nonmutational drug resistance mechanisms underlying the survival of residual cancer “persister” cells. 2- 4 The persister cell pool constitutes a reservoir from which drug-resistant tumours may emerge. Targeting persister cells therefore presents a therapeutic opportunity to impede tumour relapse. 5 In an earlier report, we found that cancer cells in a high mesenchymal therapy-resistant cell state are dependent on the lipid hydroperoxidase GPX4 for survival. 6 Here, we describe the discovery that a similar therapy-resistant cell state underlies the behavior of persister cells derived from a wide range of cancers and drug treatments. Consequently, we show that persister cells acquire a dependency on GPX4. We demonstrate that loss of GPX4 function results in selective persister cell ferroptotic death in vitro and prevents tumour relapse in vivo. These findings support targeting GPX4 as a therapeutic strategy to prevent acquired drug resistance.