This paper reports the chemical synthesis of highly-active MnO/PdCu nanocomposites coated with N-doped carbon (NC) shell using polydopamine (PDA) as the carbon source, which provides high specific surface area and pore volume. The structure and morphology of MnO/PdCu@NC nanocomposites were systematically studied. Taking advantage of the synergistic effects of PdCu alloy and MnO support, the MnO/PdCu@NC catalyst exhibited an outstanding activity toward the reduction of 4-nitrophenol (4-NP), in comparison to MnO/PdM@NC (M = Ni, Au, Ag), MnO/PdCu@PDA, and commercial Pd/C catalyst. Owing to the protection by NC shell, the as-prepared catalyst showed stable conversion efficiency of up to 90% over ten successive cycles. Considering 4-NP as one of the important organic pollutants from industrial production, the effects of various inorganic and organic species on the catalytic efficiency were further tested and most of them had negligible impact. This strategy of utilizing an N-doped carbon shell could be extended to obtain PdCu alloys supported on other metal oxides, making it applicable for applications in treatment of environmental pollutants.