Recent solar cells based on perovskite materials have the highest efficiency (>26%) in the thin-film photovoltaic industry. The KGeCl3 perovskite has emerged theoretically as a promising inorganic material. In this work, the Density Functional Theory (DFT) approach has been used to study the structural, electronic, and optical properties of the perovskite material in its cubic and monoclinic phases. The obtained negative values of the formation energies prove structural stability. The electronic properties were mainly assessed through the band structure, density of states, and effective mass. The KGeCl3 material exhibits a direct band gap with values of 0.89 and 1.49 eV for the cubic and monoclinic phases, respectively. The valence band and conduction band of all phases appear to be dominated by the p-Cl and p-Ge orbitals, respectively. The optical properties were also been explored by calculating the dielectric constant and deducing its associated parameters. The monoclinic phase presents an anisotropic nature with strong absorption, low reflectivity, and small values of energy loss in the visible range. These findings provide in-depth information suggesting that the KGeCl3 perovskites may be a promising material for photovoltaic applications.