Ni-Co-C alloy coatings with exceptional properties were fabricated via electrodeposition using an ammonium oxalate-ammonium citrate system. The optimized coatings exhibited dense crystallization with a distinct granular surface, where large particles were covered with nanoscale clusters. Additionally, C atoms primarily existed within the coatings as a solid solution, maintaining the FCC structures. Compared to binary Ni-Co coatings, the Ni-Co-C alloy coatings exhibited significantly improved hardness, wear resistance, and adhesion strength, which could be attributed to the potential strengthening effect of the C atoms. Specifically, the introduction of C atoms optimized the local charge density and electron distribution in the alloy, transforming local weak ionic bonds into strong covalent interactions, thereby enhancing the bonding capability between the corresponding atoms in the NiCo bulk.