In this paper, the mechanical and thermo-mechanical properties of glasses and glass–ceramics belonging to the Ge–Ga–Se system are studied. Pure glasses slightly transparent in the visible range up to 16 μm have been synthesized. Glass–ceramics were made using an appropriate heat-treatment time and temperature from the 80GeSe2–20Ga2Se3 base glass in order to improve the mechanical properties. The optical and mechanical properties of glasses and glass–ceramics such as hardness and toughness were investigated. X-ray diffraction (XRD) versus temperature experiments were performed to understand the crystallization evolution as a function of heat-treatment time. GeGa4Se8 and GeSe2 crystalline phases have been determined with XRD. As a result, glass–ceramics with 40% density of crystals present a very low thermal expansion coefficient (11.8 × 10−6± 0.5 K−1) and an excellent infrared transmission in the 3–5 and 8–13 μm regions.