A coverage-dependent, mean-field microkinetic model of catalytic NO oxidation, NO+0.5 O2⇌NO2, at a Pt(111) surface has been developed, based on large supercell density functional theory (DFT) calculations. DFT is used to determine the overall energetics and activation energies of candidate reaction steps as a function of surface coverage. Surface coverage is found to have a significant but non-uniform effect on the energetics, pathways, and activation energies of reaction steps involving formation or cleavage of ONO and OO bonds, and inclusion of this coverage dependence is essential for obtaining a qualitatively correct representation of the catalysis. Correlations are used to express all reaction parameters in terms of a single coverage variable θ and steady-state solutions to the resultant mean-field models are obtained in the method of DeDonder relations. At conditions representative of NO oxidation catalysis, the surface coverage is predicted to be 0.25≤θ<0.4 ML and to be controlled by equilibrium between gas-phase NO and NO2 and chemisorbed O. O2 dissociative adsorption (O2(g)→2O*) is rate limiting in the model. The DFT-based mean-field model captures many features of the experimentally observed catalysis, and its short-comings point the way toward more robust models of coverage-dependent kinetics.