Although Ag–Au alloys are vital for many industries and technological applications, thermodynamic properties data of Ag–Au solid solution are very limited, especially at low temperatures. In the present investigation, activities of silver were directly measured between 550 and 700 K by a solid electromotive force (EMF) method and AgI as the pure ionic conducting electrolyte resembled in a galvanic cell notation as -CAgAgIAlloyC(+). From the silver activity data and by employing Gibbs–Duhem integration, partial thermodynamic properties of silver and gold were calculated. Integral thermodynamic properties such as Gibbs energy of mixing, mixing enthalpy and entropy of silver and gold to form the alloys have been determined. Thermodynamic properties were also expressed by analytical equations of the partial excess properties as a function of temperature and composition, providing a user-friendly tool to generate other thermodynamic properties to be used for many purposes.