Wire-shaped supercapacitors (WSSCs) are one of the most promising energy storage devices for portable and wearable electronics. However, the large-scale preparation of fiber electrodes with high-mass loading of active-materials and the construction of wire-shaped devices with high capacity and excellent flexibility are still a big challenge. In this study, a novel scalable fiber electrode is developed by depositing manganese dioxide (MnO₂)/reduced graphene oxide (rGO) on porous nickel yarns (PNYs), named as MnO₂/rGO@PNY fiber electrodes, for the fabrication of all-solid-state flexible WSSCs. Taking advantage of the large surface area and plenty of capillary tunnels of PNYs, rGO and MnO₂ active-materials with high loading are deposited onto the surface of PNYs. Using these as-fabricated MnO₂/rGO@PNY fiber electrodes, all-solid-state flexible WSSCs are assembled with the assistance of the PVA/LiCl gel as both an electrolyte and a separator. The assembled flexible WSSCs deliver a high volume capacitance of 36.81 F cm⁻³ and retain 80.1% capacitance of the initial value after 3000 cycles under bending 45° conditions, suggesting their outstanding cycling stability and high mechanical flexibility.