Here, we have reported an excellent optical, dielectric, and electrical behavior of Cu 2 Ni 1+x Sn 1−x S 4 (CNTS) nanospheres synthesized by the facile solvothermal technique. From its structural analysis, the polycrystalline nature of the material was confirmed due to the presence of the sphalerite phase along with several secondary phases, demonstrating the structural tuning possibilities with a compositional variation. Further analysis of the electronic structure showed the presence of Cu +1 , Ni +2 , Sn +4 , and S −2 valence states in the composition. The nanoflower-like morphology made up of nanospheres remained the same even after the compositional variation and enhanced the light-trapping effect. However, the increase in the optical band gap and decrease in the refractive index showed distinctive properties with the Ni concentration variation. The frequency and temperature-dependent behavior of dielectric parameters, conductivity, impedance, and electric modulus parameters broadened the application possibilities along with the optoelectronic properties. The increase in AC conductivity with temperature enabled the hopping of charge carriers, and properties like an increase in the loss factor at a lower frequency and higher temperature made the nanomaterials favorable for devices based on high-power circuits. The decrease in impedance values indicated less current dissipation in lower-frequency regions, and the electric modulus parameter showed non-Debye-type behavior. The tunable optical, dielectric, and electrical properties of the CNTS materials widen the cutting-edge optoelectronic application possibilities.