A novel orthorhombic GdInO3:Eu perovskite red phosphor, endowed with good luminescence properties, was synthesized via a facile co-precipitation route plus controllable thermolysis. Its structural features, optical properties, and luminescent behaviors were compared with the hexagonal counterpart in detail. The two GdInO3 matrixes have relatively wide direct bandgaps (∼5.07 eV for orthorhombic perovskite and ∼5.13 eV for hexagonal phase) and low phonon energies (∼368 cm−1 for orthorhombic perovskite and ∼425 cm−1 for hexagonal contrast). Eu3+ substitution for Gd3+ occupies the C2v symmetry site without an inversion center in orthorhombic GdInO3, while the hexagonal GdInO3 provides two crystallographic positions for Eu3+ residence (∼2/3 at C3 site and ∼1/3 at C6v site). The emission spectra of two phosphors present characteristic 5D0→7FJ transitions of Eu3+ and the optimum activator concentrations are both 10 at.%. They also have good thermal stability of luminescence with relatively high similar activation energies of ∼0.25 eV. F+ center (VO∙ oxygen vacancy) is the primary defect form in the two perovskites, which has little effect on the entire red emission of orthorhombic phosphor but shifts the chromaticity coordinate of hexagonal contrast toward orange region. The orthorhombic GdInO3:Eu phosphor exhibits stronger emission intensity, a longer fluorescence lifetime, and a higher color purity than the hexagonal counterpart. Judd–Ofelt theory further confirms that orthorhombic GdInO3:Eu is an efficient red-emitting material with the relatively large parameters of Ω2 = 7.01 × 10–20 cm–2 and Ω4 = 2.85 × 10–20 cm–2.