Nitrogen, a non-metallic element, is widely abundant in nature and possesses numerous advantageous properties for metals and alloys, and supersaturated nitrogen content can be obtained through non-equilibrium rapid solidification. In this work, the microstructure and passivation properties of CoCrMo alloys prepared by the laser powder bed fusion (LPBF) technique under nitrogen and argon atmospheres were compared through multi-scale microstructural characterization combined with advanced electrochemical testing methods. Results show that the N content in LPBF N2-CoCrMo alloy (0.1839 wt%) demonstrates more than one order of magnitude higher than that of LPBF Ar-CoCrMo counterparts (0.0046 wt%). Despite comparable sub-microstructures in grain structure and dislocation cells, the LPBF N2-CoCrMo alloy demonstrates a higher corrosion potential of −0.34 VSCE and lower corrosion current density in comparison to the LPBF Ar-CoCrMo in a chloride-containing solution. Moreover, the passive film of LPBF N2-CoCrMo alloys shows a low defect density with a high-content and dense Cr2O3 layer therein. Our research calls attention to alloy design enhancement by modifying protective atmospheres during the additive manufacturing process.