In this paper, foam glass was used as an aggregate in magnesium oxychloride cement (MOC)-based mixtures. Magnesium oxychloride cement is known as a non-hydraulic, high-strength, and fire-resistant binder that can bond large amounts of miscellaneous fillers. In comparison with Portland cement, MOC has a lower environmental impact over its whole life cycle. The purpose of this paper is to modify thermal and hygric properties of MOC-based composites using lightweight mineral admixture, namely foam glass, and hydrophobic agents. The raw materials were analyzed by XRF spectroscopy and their basic properties characterized. The MOC composites were by their basic material, mechanical, thermophysical, and moisture properties described. Considerable improvement of thermal parameters of MOC composite modified with the foam glass and obvious action of surface hydrophobic agent as moisture barrier were observed. The resulting thermal-insulating, lightweight MOC composite with suitable mechanical properties can be used in the construction of thermal insulation surfaces and envelopes, ceiling or wall panels, reducing the energy consumption of buildings.