Abstract: With the rising incidence of vehicle-induced fires on bridges and the long-term exposure of cable-supported structures to corrosive environments, the safety and durability of bridge stay cables have become pressing concerns in civil engineering. High-strength parallel steel wires—the main load-carrying elements—are vulnerable to corrosion-related degradation, especially when their protective sheathing is damaged, and may experience additional thermal effects during accidental fires, resulting in accelerated material deterioration that further compromises the structural integrity and service life of the entire bridge. However, a substantial gap persists in experimental research on the residual fatigue performance of in-service corroded steel wires after fire exposure, particularly using actual bridge components. This study addresses that gap by systematically examining the residual fatigue life of corroded parallel steel wires removed from a real cable-stayed bridge after simulated fire damage. The wire specimens, extracted from a bridge built in 1995, were taken from regions near the pylons where environmental exposure had produced visible corrosion. Following ISO 8407-2021, the average corrosion depth was measured as 36.39 μm. Twenty-eight corroded wires were then exposed to 700 ℃ for 20 minutes to simulate fire temperatures typically encountered in bridge vehicle fires, followed by natural cooling, while a control group of 25 corroded but unheated wires was prepared for comparison. Fatigue tests were performed at room temperature using a GPS-100 hydraulic-servo testing machine under four stress amplitudes (300, 360, 420, and 480 MPa), with a stress ratio of 0.4 and a loading frequency of 80 Hz in accordance with GB/T 17101-2019, setting a run-out limit of two million cycles. The results showed that fire exposure markedly shortened the fatigue life of corroded wires: at higher stress amplitudes (e.g., 480 MPa), most fire-damaged specimens failed before 70,000 cycles, whereas the control group displayed considerably longer fatigue lives at all stress levels. Fractographic observations using scanning electron microscopy revealed distinct failure mechanisms: fire-damaged wires exhibited brittle fracture features, including smaller crack-initiation regions and larger instantaneous-fracture areas caused by microstructural changes such as grain coarsening and oxidation induced by high temperatures, while unheated wires showed more ductile characteristics such as shear lips and broader fatigue-crack propagation zones. Boxplot analysis indicated greater scatter at lower stress amplitudes for both groups—particularly for fire-damaged wires—due to the combined influence of corrosion and fire-induced surface degradation, with variability decreasing as stress amplitude increased. The S–N relationships plotted in double-logarithmic coordinates showed bilinear behavior with a transition point near 420 MPa for both groups, though with different tendencies: fire-damaged wires exhibited a gradual reduction in fatigue life at lower amplitudes (300–420 MPa) but a sharp decline at higher amplitudes (420–480 MPa), whereas the control group showed a steeper decline at lower stresses and a more moderate decrease at higher stresses. Empirical regression equations were developed to model the fatigue life under varying stress conditions. Overall, the study concludes that the combined effects of corrosion and fire drastically accelerate fatigue deterioration in in-service steel wires, reducing fatigue resistance and shifting the failure mode from ductile to brittle, thereby heightening the susceptibility of bridge cables under cyclic loading. The findings provide essential experimental data and predictive models for evaluating the residual fatigue life of fire-damaged bridge cables, supporting improved post-fire inspection practices, maintenance planning, and potential design-code enhancements, thereby contributing to safer and more resilient cable-supported bridge infrastructure.