GPX4 represents a promising yet difficult-to-drug therapeutic target for the treatment of, among others, drug-resistant cancers. Although most GPX4 inhibitors rely on a chloroacetamide moiety to modify covalently the protein's catalytic selenocysteine residue, the discovery and mechanistic elucidation of structurally diverse GPX4-inhibiting molecules have uncovered novel electrophilic warheads that bind and inhibit GPX4. Here, we report our discovery that diacylfuroxans can act as masked nitrile oxide prodrugs that inhibit GPX4 covalently with unique cellular and biochemical reactivity compared to existing classes of GPX4 inhibitors. These observations illuminate a novel molecular mechanism of action for biologically active furoxans and also expand the collection of reactive groups capable of targeting GPX4.