As emerging electroactive materials, the controlled synthesis of highly ordered two-dimensional (2D) conjugated coordination polymer (c-CP) films ensuring the long-range π-electron delocalization is essential for advancing high-performance (opto-)electronics. Here, we demonstrate the growth of highly crystalline 2D c-CP thin films on inert substrates by chemical vapor deposition with the assistance of ammonia (NH₃) for the first time, leveraging its deprotonation effect on ligands and competing effect as additional coordinating species. The resulting Fe-HHB (HHB = hexahydroxybenzene) films exhibit large-area uniformity and a 2 order-of-magnitude increase in crystal grain size, which translates into significant improvements in electrical conductivity (from 0.002 to 3 S/cm), charge mobility, elastic modulus, and hardness. To verify the generality of this NH₃-assisted synthesis, the contrast Cu-HHB and Cu-BHT (BHT = hexathiolbenzene) 2D c-CP thin films are also prepared and deliver significantly improved electrical conductivities from 51 to 113 and from 595 to 905 S/cm, respectively. The greatly improved crystallinity, combined with the high compatibility of the developed synthetic strategy with current device integration technologies, paves the way for developing c-CP-based electronics.