Facile synthesis of single-crystal 2D layered transition-metal nitrides (TMNs) is of crucial importance for the development of forthcoming technologies, such as superconducting, electromagnetic interference shielding, and energy-related applications. However, the fabrication of TMNs with natural 2D layered structure is thermodynamically difficult, in which stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employed alkali molten salts as catalysts to achieve facile and large-scale (over decagram) synthesis of a family of 2D layered TMNs, such as MoN_1.2, WN_1.5, and Mo_0.7W_0.3N_1.2, under atmospheric pressure. Ex-situ experiments reveal that the molten salt can lower the formation energy of 2D layered TMNs by assuring a liquid-gas synthesis and forming a TMN-salt-TMN superstructure as an intermediate. The resultant 2D layered TMNs show superior performance in hydrogen evolution reaction, demonstrating the immense potential of 2D layered TMNs for energy-related applications and beyond.