Carbon fibers (CFs) have been innovated in the application of fiber-shaped and wearable energy storage devices recently. However, time- and energy-consuming activation process under harsh conditions is generally required to modify the surface structure of the CF. Herein, a fast and effective Joule heating activation method is proposed with the nickel–cobalt layered double hydroxide-derived nanometal particles as the template. The resultant Joule heating-activated CF (JACF) demonstrates excellent capacitive performance with an electrode capacitance of 268 F g−1. After assembling into a solid-state fiber-shaped supercapacitor (FSC), the device shows both enhanced specific capacitance and energy/power densities, as well as the long cycling stability of over 5000 cycles. The Joule heating method reported in this work is time and energy saving for CF activation compared with the traditional chemical etching or high-temperature annealing processes, and it is promising for the large-scale production of high-performance fiber-shaped and wearable energy devices.