Inorganic oxides with a spinel structure play an indispensable role in various applications because of their stability and exceptional performance. This study prepared Mg5Ga2Sn2O12 ceramics using the solid-state method. TEM analysis reveals that the ceramics show local lattice distortions. When the sintering temperature is 1480 °C, the relative density and Vickers hardness of Mg5Ga2Sn2O12 ceramics are 96.8 % and 12.58 GPa, respectively. The Mg5Ga2Sn2O12 ceramics exhibit optimum microwave dielectric properties, with εr = 8.57, Q × f = 138,769 GHz, and τf = −24.7 ppm/°C. Far-infrared fitting shows that the vibration mode in the low-wave number region has a significant influence on the dielectric properties of ceramics. The P–V−L theory indicates that the Sn–O bond has the most significant influence on εr and Q × f. Given these advantages, Mg5Ga2Sn2O12 ceramics hold promise for applications in low-loss dielectric materials.