Mechanism of electrochemical oxidation of gallic acid in aqueous phosphate buffer solutions of different pH’s was studied at glassy-carbon electrode. The study was performed using cyclic, convolution–deconvolution sweep voltammetry, chronoamperometry and chronocoulometry. It gives two irreversible diffusion-controlled cyclic voltammetric waves at the entire range of pH. The electrochemical oxidation mechanism was proposed to be an ECEC-first order mechanism in which the two electron transfer steps and the two chemical follow-up deprotonation reactions are irreversible. The proposed mechanism was confirmed by digital simulation and the electrode kinetic parameters are estimated on comparing the simulated response with the experimental ones.