The fabrication of highly durable, flexible, all-solid-state supercapacitors (ASCs) remains challenging because of the unavoidable mechanical stress that such devices are subjected to in wearable applications. Natural/artificial fiber textiles are regarded as prospective materials for flexible ASCs due to their outstanding physicochemical properties. Here, a high-performance ASC is designed by employing graphene-encapsulated polyester fiber loaded with polyaniline as the flexible electrodes and bacterial cellulose (BC) nanofiber-reinforced polyacrylamide as the hydrogel electrolyte. The ASC combines the textile electrode capable of arbitrary deformation with the BC-reinforced hydrogel with high ionic conductivity (125 mS cm−1), high tensile strength (330 kPa), and superelasticity (stretchability up to ≈1300%), giving rise to a device with high stability/compatibility between the electrodes and electrolyte that is compliant with flexible electronics. As a result, this ASC delivers high areal capacitance of 564 mF cm−2, excellent rate capability, good energy/power densities, and more importantly, superior mechanical properties without significant capacitance degradation after repeated bending, confirming the functionality of the ASC under mechanical deformation. This work demonstrates an effective design for a sufficiently tough energy storage device, which shows great potential in truly wearable applications.