Electrodeposited poly(o-toluidine) (POT) on gold electrodes was investigated in a 0.5 M H2SO4 aqueous solution using cyclic electrogravimetry with in situ vis-NIR spectroscopy. This coupling of different techniques allows the electrical, color, and mass changes during the electrochemical reactions of these polymers to be correlated. Therefore, this is a powerful tool to obtain valuable information on the physical models of polymer films and their electrochemical properties. The accurate analysis of the results from these techniques showed the contribution of three different redox transitions (leucoemeraldine-polaron transition, polaron-bipolaron transition, and bipolaron-pernigraniline transition) and the participation of cation (hydrated proton), anion (bisulfate ion), and free solvent (water) transfers in these redox transitions. Moreover, the contributions of each redox transition to the current, absorbance derivative, and mass derivative were separated.