Using state-of-the-art density functional theory (DFT) based approach; we investigated the catalytic activity of electron doped C 2 N monolayer (O → N) for CO oxidation. Large surface-to-volume ratio and uniformly distributed holes of recently synthesized planar 2D C 2 N have made it a potential candidate as noble metal-free catalyst. However, pristine C 2 N monolayer is chemically inert and hinders the adsorption of O 2 and CO molecule on it. Oxygen doping in C 2 N brings additional electrons to the system and introduces donor state below E F . Thus the reactivity of O-doped C 2 N (2OC 2 N) monolayer gets significantly enhanced, thereby opening up the possibility of its usage as a catalyst. This reactive 2OC 2 N surface adsorbs an incoming O 2 molecule along with the elongation of O[sbnd]O bond, making it chemically active. Presence of this pre-adsorbed active O 2 greatly impedes the adsorption of another incoming CO, favoring Eiley-Rideal (ER) mechanism for CO oxidation.