Abstract: Bridge stay cables play a vital and indispensable role in the structural integrity and safety of cable-supported bridges. Statistical data indicates that nearly 100% of bridge stay cables exhibit varying degrees of damage, with corrosion being the most common issue. As a key component of bridge stay cables, parallel steel wires are particularly vulnerable to the detrimental effects of corrosion during their long-term service. This vulnerability progressively leads to the degradation of their mechanical properties, posing a significant threat to the overall stability and safety of the bridge structure. In recent years, with the continuous improvement of the domestic highway transportation network and rapid economic development in China, the number of motor vehicles and electric vehicles in the country has been steadily increasing. Consequently, the probability and risk of fire accidents in cable-supported bridges have risen sharply. Fire incidents not only directly damage the physical structure of the stay cables but also interact with pre-existing corrosion, creating a compounded effect. The combined impact of corrosion and fire further accelerates the degradation of the mechanical properties of the stay cables, leading to a more rapid decline in their load-bearing capacity and safety performance. This issue has become a major concern for bridge engineers and researchers, as it poses a significant challenge to the long-term durability and safety of cable-supported bridges. Despite its importance, current research, both domestically and internationally, on the degradation mechanism of the mechanical properties of parallel steel wires in corroded stay cables exposed to high temperatures remains incomplete. Similarly, the evaluation methods for assessing the mechanical properties of these corroded wires after high-temperature exposure are still under development. To gain a better understanding of the combined effects of corrosion and fire on the mechanical properties of parallel steel wires in bridges, more in-depth and comprehensive research is urgently needed. Against this backdrop, this paper focuses on 1,770 MPa brand-new bridge parallel steel wires as the research object. Through immersion testing and accelerated corrosion tests with dry-wet cycles, corrosion durations of 240 hours, 480 hours, and 720 hours were applied, producing pre-corroded steel wires with varying degrees of corrosion under simulated industrial atmospheric corrosion conditions. Subsequently, high-temperature furnace tests and tensile tests using a hydraulic universal testing machine were conducted on these pre-corroded steel wires after high-temperature exposure. The failure model was analyzed, and stress-strain curves for the 1,770 MPa pre-corroded bridge parallel steel wires post high-temperature exposure were obtained. Additionally, four mechanical property indices—elastic modulus, yield strength, ultimate strength, and fracture strain—were selected for analysis to explore the impact of corrosion and fire on the mechanical properties of parallel steel wires. By comparing the mechanical property indices of pre-corroded steel wires after high-temperature exposure with those of uncorroded parallel steel wires at room temperature, the effects of corrosion degree and fire exposure temperature on the mechanical properties of the pre-corroded steel wires were discussed. The results show that under the combined action of corrosion and fire, the mechanical properties of 1,770 MPa parallel steel wires degrade significantly. The maximum reduction coefficients for yield strength, ultimate strength, and fracture strain were 0.3758, 0.3794, and 0.3565, respectively. In conclusion, the findings of this study, based on tensile tests of pre-corroded steel wires after high-temperature exposure, provide valuable theoretical support for evaluating the performance of parallel steel wires in bridge stay cables subjected to the combined effects of corrosion and fire damage.