The introduction of alkaline earth oxides into Li₂O-Al₂O₃-SiO₂ glass components can improve the mechanical and optical performances of glass and glass–ceramics for various applications. In this research, microstructures, thermal properties, crystallization behavior, and mechanical performance changes in specific Li₂O-Al₂O₃-SiO₂ glass with the introduction of different alkali earth oxides, MgO, CaO, SrO, and BaO, were investigated. From Raman and NMR spectra microstructure analysis, it was confirmed that the addition of MgO could compete with Al as a network former and charge compensator, while increasing the bridging oxygen number with Si and affecting the chemical shift in ²⁹Si. Meanwhile, the glass structures slightly changed due to the introduction of CaO, SrO, and BaO, with larger ionic radii. Meanwhile, the glass transition and first crystallization temperatures increased due to MgO introduction and then decreased with larger-radii alkali earth oxides’ addition, due to different glass network connectivity. After heat treatment, the crystal phases in the glass–ceramics changed with the introduction of alkaline earth oxides. The main crystal phases varied from Li₂Si₂O₅, SiO₂, and LiAlSi₄O₁₀ in glass without alkali earth oxide introduction; to SiO₂, Li_xAl_xSi_3−xO₆, and MgAl₂Si₄O₁₂ in glass with MgO addition; to SiO₂ and Li_xAl_xSi_3−xO₆ with CaO addition; to SiO₂, LiAlSi₄O₁₀, and Li₂SiO₃ for glass with SrO addition; and further to Li₂SiO₅, SiO₂, and LiAlSi₄O₁₀ for glass with BaO addition. Moreover, in the mechanical performance of the glass–ceramics, the Vickers hardness and elastic modulus reached a maximum of 8.61 GPa for glass with MgO and 90.12 GPa for glass with BaO modification, respectively, probably due to different crystal phases. More importantly, the crack resistance values presented a large increase for MgO glass and MgO- or CaO-modified glass–ceramics.