<p>The CuO/SnO₂ nanocomposites (NCs) were synthesized using a simple hydrothermal process to produce high-performance photocatalytic and electrochemical applications. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FESEM-EDX), high-resolution transmission electron microscopy with selected area electron diffraction (HRTEM-SAED), UV–visible diffuse reflectance spectroscopy (UV-DRS), and X-ray photoelectron spectroscopy (XPS) investigations were used to characterize the properties of the prepared NCs. The XRD patterns ensured tetragonal and combined (monoclinic/tetragonal) phases for SnO₂ and CuO/SnO₂ composites, respectively. The estimated crystallite sizes were in the nanometer range and decreased from 29 to 21&#xa0;nm with increasing CuO content. FTIR spectra were used to identify the metal oxide peaks that corresponded to SnO₂ and CuO. The FESEM image for 1CS7 NC shows spherically agglomerated particles, whereas for 2CS7 and 3CS7, NCs exhibit a few rod structures along with spherical-shaped particles. The HRTEM images revealed the spherical morphology for optimized 1CS7 NCs. The oxidation states of synthesized CuO/SnO₂ composites were confirmed using XPS investigations. Utilizing Kubelka–Munk method, the band gap values were determined for 1CS7, 2CS7, and 3CS7 NCs that rise from 2.66, 3.33, and 3.50&#xa0;eV, respectively. The photocatalytic behavior of CuO/SnO₂ NCs was studied by degrading methyl violet (MV) dye under solar irradiation for 70&#xa0;min. The 1CS7 NC had higher degradation efficiency (91%) than other synthesized NCs. Furthermore, at a current density of 0.5 Ag⁻¹, the 1CS7 electrode exhibited a specific capacitance of 770 Fg⁻¹, and this electrode shows enhanced cyclic stability, maintaining 93.4% up to 2000 cycles. This investigation reveals that the 1CS7 composite is the outstanding material for photocatalytic and supercapacitor applications.</p>