With the rapid development of infrared technology and the wide applications of infrared optical components, the demand for infrared optical materials has risen significantly. Chalcogenide glass has been considered as one of the most popular infrared optical materials because of its wide infrared transmission range, high refractive index, low phonon energy, good rheological properties, low cost, etc. In this work, a new type of Ga₂S₃-Sb₂S₃-Ag₂S chalcogenide glass system is reported, and its glass forming domain is determined. The thermal stability and optical property, mid-infrared (MIR) emission of rare earth dopant, and fiber-forming property for the glasses are studied. The potential applications of the glasses in the MIR region are also evaluated. The experimental results show that the Ga₂S₃-Sb₂S₃-Ag₂S system has a glass forming domain of ~10%–30% Ga₂S₃, ~60%–80% Sb₂S₃ and ~0–15% Ag₂S (all in molar percentage). These glasses have a wide infrared transmission range of ~0.8–13.5 μm, relatively high linear refractive indices of~2.564–2.713 (at 10 μm), and relatviely large third-order nonlinear refractive indices of ~9.7×10^–14–15.7×10^–14 cm²/W (at 1.55 μm). These excellent properties make the Ga₂S₃-Sb₂S₃-Ag₂S glass promising material in the fields of infrared thermal imaging and nonlinear optics. Under the excitation of 1.32 µm laser, the rare earth dopant Dy³⁺ shows strong 2.91 μm and 4.41 μm MIR emissions in the glass. According to the J-O theory, the three strength parameters (Ω₂, Ω₄, Ω₆) of Dy³⁺ in 0.05% weight of Dy³⁺ doped 20Ga₂S₃-75Sb₂S₃-5Ag₂S glass are 7.38×10^–20 cm², 2.24×10^–20 cm² and 0.75×10^–20 cm², respectively. The quantum efficiencies of the 2.91 μm and 4.41 μm emissions are calculated to be 76.6% and 70.8%, respectively, while the stimulated emission cross sections of those two bands are 1.27×10^–20 cm² and 1.43×10^–20 cm², respectively. The fiber based on 20Ga₂S₃-75Sb₂S₃-5Ag₂S: 0.05% Dy³⁺ core glass and 20Ga₂S₃-70Sb₂S₃-10Ag₂S cladding glass is fabricated by rod tube method. The fiber has good transmission performance in the 2–8 μm wavelength range, and the minimum loss is ~3.5 dB/m at 5.7 μm. The Dy³⁺ ions show intense 2.93 μm and 4.45 μm MIR emissions in the fibers under 1.32 μm excitation. These results indicate that the Dy³⁺ doped Ga₂S₃-Sb₂S₃-Ag₂S glass fiber can be a promising candidate for MIR fiber laser medium.