This paper presents the clear evidence of nonthermal plasma-induced synergism of biogas reforming studied at 5 kPa. Reactant conversion and product yield were increased by superposing dielectric barrier discharge (DBD) to the Ni-based supported catalyst at a fixed temperature. Reforming performance was further promoted by increasing the operating frequency from 12 to 100 kHz, while maintaining the catalyst temperature (600 degrees C) as well as specific energy input (SEI = 1.37 eV/molecule). Kinetic analysis revealed the key rate-determining step, i.e. dissociative CH4 activation is clearly promoted by plasma catalysis. However, excessive CH4 activation accelerated coke formation when CH4/CO2 > 1. Reforming characteristics were correlated with the electrical properties of packed-bed DBD, showing the increase in discharge current is critically important to strengthen plasma-induced synergism, while an increase in mean electron energy seems to have a minor effect. Moreover, discharge properties were correlated with electron collision kinetics; the vibrationally excited CH4 and CO2 play a key role in plasma catalysis of biogas reforming.