The nanocrystalline copper aluminate (CuAl2O4) has been successfully synthesized by a simple, economical, and environmentally friendly solid-state mechanochemical (MCH) method. The prepared sample was characterized by a variety of suitable methods employed, including scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), Fourier transform infrared spectroscopy (FT-IR), and X-ray powder diffraction (XRD). The material's average particle size was 55 nm and stoichiometric. CuAl2O4 has been found to exhibit potent photocatalytic activity toward indigo carmine (IC) when subjected to UV light. Under UV radiation, 10 mg CuAl2O4 leads to 99 ± 1% degradation of an 8 ppm IC dye solution among 2 ppm, 4 ppm, 6 ppm, 8 ppm, and 10 ppm in 25 min. In addition, a prospective liquid chromatography-mass spectrometry (LC-MS) technique is identified in the current work, which provides potential routes for the photocatalytic breakdown of IC. Even after five consecutive cycles, the photocatalyst showed remarkable reusability and stability.