Bulk metallic glasses with a maximum diameter of 2.5–5 mm were formed in Mg75Cu5Ni10Gd10, Mg70Cu15Ni5Gd10, and Mg65Cu20Ni5Gd10 systems by copper mold casting. There is a clear tendency for glass-forming ability (GFA) to increase with increasing solute content. These bulk glassy alloys exhibit a large supercooled liquid region (ΔTx) of 44–64 K, indicating high thermal stability of the supercooled liquid. The Young’s modulus, fracture strength, elastic elongation limit, and plastic strain are in the range of 54–59 GPa, 854–904 MPa, 1.50–1.55%, and 0.10–0.20%, respectively. The Mg65Cu20Ni5Gd10 alloy exhibited the highest values of Young’s modulus and strength, while the largest plastic strain was obtained for the Mg75Cu5Ni10Gd10 alloy. The bulk Mg–Cu–Ni–Gd-based metallic glasses exhibited distinct enhanced corrosion resistance compared to Mg65Cu25Gd10 glassy alloy in NaCl aqueous solutions. The fabrication of the Mg-based bulk glassy alloys exhibiting a high strength level of about 900 MPa and plastic strains of ∼0.2%, in conjunction with good corrosion resistance, indicates that the Mg-based bulk glassy alloys may be used as a new generation of structural material.