The main challenge in water electrolysis, an appealing technique to alleviate future energy crisis, is the design of efficient electrocatalysts for hydrogen evolution reaction (HER). On the basis of an interface self-assembly approach, we synthesize mesoporous nitrogen-doped carbon/Mo₂C/reduced graphene oxide nanohybrids (denoted as mNC-Mo₂C@rGO), which represent a new type of two-dimensional Mo₂C/carbon hybrid nanomaterials and possess a sandwichlike structure with well-defined mesopores. The method involves the co-self-assembly of spherical micelles formed from polystyrene-block-poly(ethylene oxide), pyrrole (Py) monomers, and molybdate ions (Mo₇O₂₄ ^6-) on GO surfaces in aqueous solution, followed by polymerization of Py and calcination of the nanocomposites at 900 °C under nitrogen atmosphere. The resultant mNC-Mo₂C@rGO nanosheets possess high N contents, large specific surface areas (SSAs), and 4 nm Mo₂C particles well-distributed in the mesoporous carbon matrix. The Mo₂C content is controllable in the range of 18.4-42.4 wt % by adjusting the feed amount of Mo₇O₂₄ ^6-. In particular, mNC-Mo₂C@rGO with an SSA of 344 m²/g and a Mo₂C content of ca. 28 wt % exhibits the highest HER catalytic activity in 1 M KOH electrolyte, with a 95 mV overpotential at 10 mA/cm², a Tafel slope of 49.8 mV/dec, and a long-term stability of 60 h at 20 mA/cm². This study blazes a trail for the synthesis of new functional nanomaterials with potential applications as efficient HER electrocatalysts.