Glycine has emerged as a promising, environmentally benign alternative to cyanide for gold leaching. However, the thermodynamic stability of gold-glycinate complexes under elevated temperatures and pressures remains insufficiently quantified. In this study, the revised Helgeson-Kirkham-Flowers (HKF) equation of state was applied to evaluate the temperature- and pressure-dependent thermodynamic properties of aqueous species in the Au-Gly-H₂O system. Standard partial molal Gibbs free energies were calculated over the temperature and pressure of 298-363 K and 1-50 bar, respectively. Missing thermodynamic properties for aqueous Au(OH)₃ were estimated through regression based on correlations among trivalent metal hydroxide complexes and incorporated into the HKF framework. Temperature-dependent Eh-pH diagrams reveal that increasing temperature significantly expands the stability field of the Au(Gly)₂- complex toward lower oxidation potentials and broader pH ranges. In contrast, pressure variations up to 50 bar revealed a negligible influence on the stability of gold species exposed to glycine and water. This work provides a preliminary thermodynamic assessment of the Au-Gly-H₂O system between experimental observations and thermodynamic analysis in glycine-based gold leaching. The developed framework offers a preliminary thermodynamic tool, which, when coupled with future experimental validation and activity-coefficient modeling, may support optimization of glycine-based gold leaching and related lixiviant systems.