Enterohemorrhagic Escherichia coli (EHEC) causes thrombotic microangiopathy, yet the red blood cell (RBC)-centered mechanism has remained unclear. We identify the RTX-family hemolysin EhxA as the driver of RBC-mediated thrombogenesis. Deletion of ehxA abolishes Ca²⁺ influx, phosphatidylserine (PS) exposure, progression from discocyte to echinocyte to spherocyte, thrombin generation, RBC-endothelium adhesion, and RBC aggregation. Genetic complementation restores these readouts to wild type, and purified EhxA in bacteria-free assays recapitulates them while localizing to intact RBC membranes. By contrast, Δstx2 mutants do not elicit these RBC phenotypes, distinguishing this pathway from Shiga toxin-dependent effects. Multiple regression quantifies the link between PS exposure, morphology, and procoagulant outputs. In rats, infection with wild type increased RBC remodeling and venous thrombosis, whereas infection with ΔehxA did not. Together, the data define an EhxA-Ca²⁺-PS pathway that drives RBC structural remodeling and procoagulant activation during EHEC infection and nominate RTX toxins as targets for preventing toxin-induced coagulopathies.