With the aid of supercritical carbon dioxide (scCO2), which has gas-like diffusivity, extremely low viscosity, and near-zero surface tension, highly dispersed Pd nanoparticles (NPs) can be directly synthesized on carbon nanotubes (CNTs). Due to the excellent wettability between scCO2 and the carbon surface, the deposited Pd NPs are uniformly distributed and tightly anchored on CNTs, which do not require pretreatment. The decoration density of NPs on carbon can be easily regulated by adjusting the Pd(hfa)2 precursor to CNT ratio, with the particle size of Pd remaining almost constant (no significant crystal growth or aggregation occur). The prepared Pd NPs on CNTs show excellent activity toward hydrogen spillover as compared to those fabricated using conventional processes. With the superior utilization of NPs, a smaller amount of Pd is required, reducing both costs and environmental impact. The proposed scCO2-assisted protocol for constructing NP/carbon nanostructures is effective, versatile, and potentially scalable, making it useful for further exploitation in a variety of applications.