Both CO and NO are important, environmentally harmful industrial gases. The reaction of CO and NO to produce CO and N has stimulated much research interest aimed at degradation of these two gases in a single step. Herein, we report an efficient CO oxidation by NO catalyzed by a (PNN)Ru-H pincer complex under mild conditions, even with no added base. The reaction is proposed to proceed through a sequence of O-atom transfer (OAT) from NO to the Ru-H bond to form a Ru-OH intermediate, followed by intramolecular OH attack on an adjacent CO ligand, forming CO and N. Thus, the Ru-H bond of the catalyst plays a central role in facilitating the OAT from NO to CO, providing an efficient and novel protocol for CO oxidation.