Electrocatalysts are increasingly being used for the production of clean energy. In the past few decades, a wide range of two-dimensional (2D) materials have shown great potential in replacing noble metal catalysts for various electrocatalytic reactions. However, development of alkaline hydrogen evolution technology (a kinetically sluggish process for the conversion of electricity to hydrogen fuel in water electrolyzes) is greatly hindered due to the lack of active candidate materials and mechanistic understanding. In this work, we prepared a hybrid material of 2D graphitic carbon nitride and 2D molybdenum nitride (C3N4@MoN) using an interface engineering strategy. The resultant material had a well-designed heterostructure and unique electronic structure. The intimate interaction of both inert graphitic carbon nitride (g-C3N4) and MoN surfaces induced a highly active interface with tunable dual active sites for alkaline HER. Thus, the 2D C3N4@MoN hybrid exhibited highly efficient electrocatalytic performance which is better than most of the recently reported non-noble metal catalysts. The combination of experimental characterization with density functional theory calculations shows that the enhanced activity originates from the synergy between the optimized hydrogen adsorption energy on the g-C3N4 sites and enhanced hydroxyl adsorption energy on the MoN sites.