 In this work, we report the fabrication of a high-voltage flexible supercapacitor that is able to store energy harvested from a 3D-printed wearable human motion energy harvester and provide power supply to other wearable devices. To bestow the electrode with flexibility, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) is incorporated with single-walled carbon nanotube (SWCNT) as electrode material, which dramatically decreases its Young’s modulus. Furthermore, the supercapacitor is sandwiched between self-healing layers that protects the device from mechanical failure caused by motion when mounted on the human body as wearable device. Owing to the use of ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), as the electrolyte, the supercapacitor can be charged up to 2.5 V. This wide electrochemical window, with low equivalent series resistance (ESR), enhances the power and energy densities of the supercapacitor to 11 kW kg− 1 and 23 Wh kg− 1. The device presents excellent flexibility and mechanical durability. We realized a wearable self-powered and self-sustaining system by the integration of the as-prepared supercapacitor with a 3D-printed mechanical energy harvesting knee brace. Harvested energy generated by a tester wearing the system was sufficient to light up an LED light in a demonstration.