The solid solution of a (1−x)PbZrO3–xPb(In1/2Nb1/2)O3 (PZ–PIN) system, with x=0.00–0.50, was synthesized using the wolframite precursor method. The effects of the PIN content on the crystal structure, and the electrical and thermal properties of a PbZrO3 ceramic were investigated using X-ray diffraction, dielectric spectroscopy, hysteresis measurement, and differential scanning calorimetry techniques. Furthermore, the morphology and grain size were determined using scanning electron microscopy. The results indicated that the pure perovskite phase was obtained for all compositions, and the solid solution, PZ–PIN, changed from orthorhombic to rhombohedral symmetry when the amount of PIN increased. A ferroelectric intermediate phase began to appear between the paraelectric and the antiferroelectric phases of pure PZ, with increasing PIN content. The temperature range width of the ferroelectric phase also increased continuously with increasing PIN. At room temperature, the polymorphic phase transition (PPT) was identified from the orthorhombic to the rhombohedral phase in (1−x)PZ–xPIN at the composition, x=0.40. The ceramics (x=0.40) with PPT close to room temperature exhibited excellent electrical properties (ɛrmax=33240 and Pr=26.94 μC/cm2).