Kinetic interactions between H2 and CO over PdO, a widely used catalyst in combustion systems, were studied experimentally and numerically. Global reaction parameters of H2 and CO oxidation over PdO were extracted from wire microcalorimetry experiments at atmospheric pressure in the temperature range 380–800 K, based on which a full catalytic reaction mechanism was developed. Comparison of ignition temperatures and heat release rates of different H2/CO blends along with density functional theory (DFT) simulations revealed complex physicochemical coupling of the H2 and CO catalytic oxidation pathways. The coupling evolves from an inhibiting effect of one fuel component onto the other due to their competition for surface adsorption sites and a direct repelling mechanism between the co-adsorbed H(s) and CO(s), to a promoting effect at sufficiently high temperatures caused by alleviated O(s) surface blocking. Implications of the H2–CO kinetic coupling to the operation of practical power generation systems are outlined.