Kinetic ignition enhancement of H2 counterflow diffusion flames by a non-equilibrium plasma discharge of air and ultra-lean pre-mixtures was studied experimentally and computationally through the development of a well defined counterflow system. Measurements of the ignition temperatures, major species and sensitivity analyses were conducted to identify the key kinetic enhancement pathways. It was found that the competition between the catalytic effect of NOx and the inhibiting effects of H2O and CH4 controlled the ignition processes in the system. With air as the oxidizer, ignition was enhanced from the plasma produced NOx. With H2 ultra-lean pre-mixtures as the oxidizer, H2O formation significantly increased the ignition temperature. However with plasma activation, the inhibiting effect of H2O was significantly reduced because of the dominant role of NOx. With CH4 ultra-lean pre-mixtures as the oxidizer, the ignition temperatures increased due to the quenching of radicals by H2O or CH4, depending upon the strain rate. However, it was also found that the inhibiting effect was significantly decreased with plasma activation. Unlike vitiated air ignition, plasma enhanced ignition for fuel-air mixtures can suppress the inhibiting effects of H2O and CH4 because of the overwhelming catalytic NOx effect at low temperatures and the conversion to less species with less ignition inhibiting effects.