<p>Using density functional theory, this analysis investigated the multifunctional properties of halide double perovskite compounds Rb₂AgXCl₆ (X = Ti, Sb, and In). While elastic constants, Pugh's ratio, and Poisson's ratio showed mechanical robustness and ductility, geometrical relaxation confirmed their cubic phase stability. Band gaps between 1.84 and 2.18 eV were found by analyzing the electronic band structure, placing them in the visible spectrum. Absorption spectra, dielectric response, conductivity, reflectance, and refractive index were among the optoelectronic characteristics that showed strong absorption, low reflectance, and minimal energy dissipation. This optical profile highlights their intrinsic suitability as active absorber layers within photovoltaic cells and photodetectors, as benchmarked against established perovskite standards. The direct-bandgap indium analogue emerges as highly promising for light-emitting applications. Additionally, effective p-type conduction and promising energy conversion efficiency were highlighted by the thermoelectric transport parameters, which were assessed using the Seebeck coefficient, the electronic power factor, and the figure of merit. In conclusion, the results show that Rb₂AgXCl₆ compounds combine adjustable optoelectronic characteristics, structural integrity, and potential thermoelectric performance, making them attractive options for advanced optoelectronic technologies and sustainable energy solutions.</p>