A steady-state kinetic model for the NH3-SCR and NH3 oxidation by a monolithic Cu-exchanged chabazite (Cu-CHA) catalyst has been developed by a combination of flow reactor experiments and kinetic modeling with an in-house computational code. Arrhenius parameters for NH3-SCR and NH3 oxidation and reaction orders with respect to H2O and O-2 are collected using a Cu-CHA catalyst coated onto a honeycomb cordierite substrate. While H2O is shown to affect NH3-SCR and low temperature NH3 oxidation to N-2 negatively, it promotes high temperature NH3 oxidation to NO. By a combination of calculations for heat and mass transfer and the parameters of the monolithic catalyst, a kinetic model is proposed. The model is validated with eight new experiments for NH3-SCR and NH3 oxidation. The calculated conversions of NO and NH3 are in good agreement with the experimental values over a wide range of temperatures (150 degrees C-600 degrees C), indicating that the model can be used for predicting the catalyst performance of the monolithic Cu-CHA for NH3-SCR.