Here, we estimate the amount of reactive nitrogen available for the origin and maintenance of life on early Mars. Lightning formed in explosive volcanic clouds is proposed as a source of nitrogen fixation. Volcanic lightning was simulated in the laboratory using a laser induced plasma. We derived the chemical composition of the gas mixture from an accretion model of Mars and the nitrogen content of Martian meteorites. The mixture contained CH4, H2, H2O and N2 in variable amounts to represent the range of C/N ratio measured in the Martian meteorites. For comparison, other endogenous and exogenous sources of fixed nitrogen in early Mars were calculated. Our experimental simulations indicate that volcanic lightning may be the only endogenous source of hydrogen cyanide (HCN) forming about 107 kg yr-1 of this compound. The total budget of fixed nitrogen for early Mars would be ~10 kg yr-1 km-2, similar to that calculated for early Earth.