Despite the rapid development and enormous success of organic–inorganic hybrid halide perovskites (AB′X₃), such as CH₃NH₃PbI₃ as absorbers for perovskite-based solar cells (PSCs), the commercial applications of photovoltaic techniques still face several challenges, such as decomposition when exposed to light and moisture, and lead toxicity. On the other hand, the double perovskites (A₂B′B″X₆) are derived from the AB′X₃ when half of the octahedrally coordinated B′-cations are partially replaced by the suitable B″-cations. They are attracting attention due to a new design strategy to replace Pb²⁺ ions with the couple of a monovalent M⁺ ion and a trivalent M³⁺ ion, leading to a new family of quaternary double perovskites. In this way, we aim to synthesize and characterize Cs₂AgSbCl₆ powdered samples, designed for solar cell applications. The crystalline phase and morphological features are investigated by X-ray powder diffraction (XRPD), neutron powder diffraction (NPD), scanning electron microscopy (SEM) in complement with UV–vis spectroscopy, showing a suitable band gap of 2.7 eV. The solution synthesis method proved to be efficient in obtaining polycrystalline-Cs₂AgSbCl₆ samples in a cubic ordered phase. DFT calculations also provided insights on the vibrational properties of Cs₂AgSbCl₆, corroborating the experimental data and elucidating the optical activity of Raman and infrared modes.