We report the preparation and hydrogenation performance of a single-site palladium catalyst that was obtained by the anchoring of Pd atoms into the cavities of mesoporous polymeric graphitic carbon nitride. The character- ization of the material confirmed the atomic dispersion of the palladium phase throughout the sample. The catalyst was applied for three-phase hydrogenations of alkynes and nitro- arenes in a continuous-flow reactor, showing its high activity and product selectivity in comparison with benchmark cata- lysts based on nanoparticles. Density functional theory calcu- lations provided fundamental insights into the material struc- ture and attributed the high catalyst activity and selectivity to the facile hydrogen activation and hydrocarbon adsorption on atomically dispersed Pd sites.