There has been extensive research on microwave dielectric materials considering their application in 5G and 6G communication technologies. In this study, the sintering temperature range of Mg2TiO4–CeO2 (MT-C) ceramics was broadened using a composite of CeO2 and Mg2TiO4 ceramics, and their microwave dielectric performance was stabilized. Low-loss MT-C composite ceramics were prepared using the solid-phase reaction method, and their microwave dielectric properties, microscopic morphologies, and phase structures were investigated. The proposed MT-C ceramics contained Mg2TiO4 and CeO2 phases; their average grain size was maintained at 2–4 μm in the sintering temperature range of 1275–1425 °C, and the samples were uniformly dense without porosity. The cross-distribution of Mg2TiO4 and CeO2 grains in the samples inhibited the growth of ceramic grains, providing uniform and dense surfaces. The dielectric loss of MT-C ceramics remained constant in the temperature range of 1300–1425 °C at 9 × 10−4 (8.45 ≤ f ≤ 8.75 GHz). As opposed to the base material, MT-C ceramics are advantageous owing to their wide sintering temperature range and the stable microwave dielectric properties, and there are suitable substrate materials for further industrial applications.