The importance of catalytic CO oxidation for exhaust gas processing has inspired the development of efficient and durable catalysts that can be operated at low temperatures, as exemplified by supported noble metals. However, most of the related studies have neglected the potential effects of co-present exhaust gas components, such as NO. Herein, we compared the performances of platinized and bare TiO2 for the ambient-temperature (photo)catalytic oxidation of CO by O2 in the co-presence of NO and used in situ Fourier transform infrared spectroscopy to elucidate the effects of platinization on the efficiency and mechanism of this oxidation. Catalytic CO oxidation was accompanied by competitive NO oxidation both in the dark and under ultraviolet (UV) illumination. In the dark, Pt/TiO2 achieved a higher CO removal efficiency than bare TiO2, which was ascribed to the enhanced adsorption of O2 and CO and the inhibition of NO overoxidation (mainly the oxidation of the monodentate nitrito form to the bidentate nitrate form). Under UV illumination, Pt/TiO2 efficiently promoted CO oxidation at photocatalytically active sites (Pt0–CO) by suppressing NO overoxidation and increasing the reduction of NO to N2O. Hence, the enhanced CO oxidation performance of Pt/TiO2 was due to its ability to control NO oxidation and reduction at ambient temperature, which presents a new strategy for the design of low-temperature CO oxidation catalysts.