The characteristics of diffuse glow discharges in pure argon and the Ar + 1%N2 mixture at pressures of 2–80 Torr were studied experimentally and numerically. The discharge operated in a molybdenumglass tube with an inner diameter of 2.8 cm and interelectrode distance of 75 cm. The current-voltage characteristic of the discharge and the populations of the N2(B3Γ g ) and N2(C3Γ u ) states were measured. It is shown that, at relatively low pressures (P < 10 Torr), the current-voltage characteristic of a discharge in the argon-nitrogen mixture lies higher than that in pure argon. In contrast, at higher pressures (P > 15 Torr), the current-voltage characteristic of a discharge in the mixture lies lower than that in pure argon. As the pressure increases, the effect of the reduction in the discharge voltage becomes more pronounced. A self-consistent zero-dimensional kinetic model is developed that allows one to calculate the characteristics of the positive column of a discharge in pure argon and Ar:N2 mixtures under the conditions of high vibrational excitation of nitrogen. A detailed description of the model is presented, and the calculated results are compared with experimental data. The model adequately reproduces the observed change in the current-voltage characteristic in Ar and the Ar + 1%N2 mixture with increasing gas pressure. It is shown that the main ionization mechanism in the Ar + 1%N2 mixture at moderate pressures is the associative ionization of excited nitrogen atoms.