Ultrafine noble metal nanoparticles decorated on onion-like carbon (OLC) were successfully prepared without any reductant or surfactant. Particularly, the as-prepared Pt–OLC nanocomposite not only exhibited superior electrocatalytic activity and stability for the hydrogen evolution reaction as compared with the commercial 20% Pt/C, but also showed enhanced supercapacitor performance with a specific capacitance almost four times larger than that of OLC. Notably, the C–O functional groups on the surface of OLC will increase after the reaction because of the oxidation by O₂ and chloroplatinic acid, which is very useful for the reuse of OLC and helpful for the decoration of noble metal nanoparticles on OLC. This work provides a simple and straightforward method for the facile preparation of metal composite nanocatalysts with high catalytic activity.