A novel, cheap and highly efficient Ni-Co/Mo₂C/Co₆Mo₆C₂@C nanocomposite has been successfully constructed through simple one-step carbonization method in a nitrogen atmosphere. Polyethyleneimine in the precursor can effectively anchor molybdenum-based Keggin-type polyoxometallate and NiCo-layered double hydroxide through electrostatic and coordination interactions, which avoids the aggregation of catalyst particles during the pyrolysis process. After optimization, the obtained Ni-Co/Mo₂C/Co₆Mo₆C₂@C possesses small size (3–8 nm), large specific surface area and hierarchical pore structure. More importantly, Ni-Co/Mo₂C/Co₆Mo₆C₂@C presents remarkable hydrogen evolution reaction activity with low overpotentials in 0.5 mol·L^–1 H₂SO₄ (102.3 mV) and 1 mol·L^–1 KOH (95 mV) to afford the current density of 10 mA·cm^–2, as well as small Tafel slopes of 82.49 and 99.92 mV·dec^–1, respectively. Simultaneously, this catalyst also shows outstanding stability for 12 h without a significant change in current density. The excellent catalytic performance of Ni-Co/Mo₂C/Co₆Mo₆C₂@C can put down to the synergistic effect between multiple components and the small size of the catalyst. This work provides unique insights into the preparation of efficient transition metal-based catalysts for HER.