In this work, formation in the binary and ternary systems of the FeIII metal ion with gallic acid and glycine was investigated by means of potentiometry, conductometry, polarography, and UV−visible absorption spectroscopy techniques at 25 °C and in I = 0.10 mol·dm−3 NaNO3. The protonation equilibria of gallic acid and glycine were investigated and discussed. The acidity constants of gallic acid and glycine were determined and used for determining the stability constants of the binary and ternary complexes formed in the aqueous medium under the experimental conditions. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The concentration distribution of the various complex species in solution was evaluated and discussed. The solid binary [FeIII−gallic acid] and ternary [FeIII−gallic acid−glycine] complexes were synthesized and characterized by elemental analysis, FT-IR, 1H NMR, and 13C NMR spectroscopy.