We present a combined study of experimental and computational work for a dielectric barrier discharge (DBD) used for CH4 conversion into H2. More specifically, we investigated the influence of N2 as an impurity (1–50,000 ppm) and as additive gas (1–99%) on the CH4 conversion and H2 yield. For this purpose, a zero-dimensional chemical kinetics model is applied to study the plasma chemistry. The calculated conversions and yields for various gas mixing ratios are compared to the obtained experimental values, and good agreement is achieved. The study reveals the significance of the N2(A3) and N2(a'1) metastable states for the CH4 conversion into H2, based on a kinetic analysis of the reaction chemistry.