A new class of hierarchical α-Fe₂O₃/poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell Janus-type hybrid nanoparticles (HNPs) was successfully synthesized using sonochemical, liquid–liquid diffusion-assisted crystallization, and vapor deposition polymerization methods. The synthesized α-Fe₂O₃/PEDOT HNPs exhibited several unique properties, including a large surface area, high conductivity, excellent electrochemical properties, and high chemical stability. In addition, the α-Fe₂O₃/PEDOT HNPs reduced the dynamic resistance of electrolyte ions, and enabled high charge–discharge rates and stable expansion of the cell voltage up to 2.0 V, thereby enabling high-performance supercapacitance. These results were attributed to synergetic effects between iron oxide (core structure with a negative working potential window) and PEDOT (shell structure with a positive working potential window), resulting in performance enhancements of specific capacitance (252.8 F g⁻¹) and energy (136.3 W h kg⁻¹) and power densities (10 526 W kg⁻¹). The specific capacitance exhibited 92% retention after 1000 cycles. Additionally, a flexible supercapacitor based on the α-Fe₂O₃/PEDOT HNPs was successfully demonstrated using a hydrogel electrolyte. The fabricated all-solid-state symmetrical supercapacitor produced superior electrochemical and mechanical performance, even after several bending motions.