<p>Halide-based double perovskites are gaining popularity as optoelectronic materials due to their tunable bandgaps and enhanced stability over simple perovskites. These compounds also have intriguing thermoelectric properties, making them ideal candidates for efficient thermoelectric power conversion systems. We employed density functional theory (DFT) to study the electrical, optical, and thermoelectric properties of novel Rb₂XAgF₆ (X = Ga and In) halide-based double perovskites in the cubic phase. The full-potential linearized augmented plane wave approach was used in this investigation. The density of state investigation validates these compounds’ electronic characteristics. The linear optical properties were used to determine the optical behavior of these materials. The results of these materials’ thermoelectric characteristics and specific temperature ranges are reported. It was demonstrated that these materials possessed remarkable properties that would make them ideal for important applications in the realms of optical, thermoelectric, and electric devices.</p>