Using melt-derived LD glass powders and 5–20 M NaOH solutions, porous lithium disilicate (Li₂Si₂O₅, LD) glass–ceramics were prepared by the cold sintering process (CSP) associated with the post-annealing technique. In this novel technique, H₂O vapor originating from condensation reactions between residual Si–OH groups in cold-sintered LD glasses played the role of a foaming agent. With the increasing concentration of NaOH solutions, many more residual Si–OH groups appeared, and then rising trends in number as well as size were found for spherical pores formed in the resultant porous LD glass–ceramics. Correspondingly, the total porosities and average pore sizes varied from 25.6 ± 1.3% to 48.6 ± 1.9% and from 1.89 ± 0.68 μm to 13.40 ± 10.27 μm, respectively. Meanwhile, both the volume fractions and average aspect ratios of precipitated LD crystals within their pore walls presented progressively increasing tendencies, ranging from 55.75% to 76.85% and from 4.18 to 6.53, respectively. Young’s modulus and the hardness of pore walls for resultant porous LD glass–ceramics presented remarkable enhancement from 56.9 ± 2.5 GPa to 79.1 ± 2.1 GPa and from 4.6 ± 0.9 GPa to 8.1 ± 0.8 GPa, whereas their biaxial flexural strengths dropped from 152.0 ± 6.8 MPa to 77.4 ± 5.4 MPa. Using H₂O vapor as a foaming agent, this work reveals that CSP associated with the post-annealing technique is a feasible and eco-friendly methodology by which to prepare porous glass–ceramics.