A critical evaluation and thermodynamic optimization of all available experimental data of the Li₂O-Al₂O₃-SiO₂ system at 1 atm pressure was performed for the first time to obtain a set of consistent Gibbs energy functions of all phases in the system. The Gibbs energy of liquid oxide solution was described using the Modified Quasichemical Model considering the formation of LiAlO₂ associate component for charge compensation effect. Various solid solutions were modeled based on their crystal structures. The obtained Gibbs energy functions can reproduce all available and reliable experimental data from 298 K to above liquidus temperatures. With the Gibbs energy description for each phase, any phase diagram and thermodynamic properties of this system and its sub-binaries can be calculated. The present thermodynamic database was applied to the thermodynamic analysis of the selective crystallization in glass-ceramics.