<p>This study presents an investigation into the properties of Ba₂XIO₆ (X = Li, K, and Rb) double perovskites using the WIEN2k computational code within the density functional theory (DFT) framework. First-principles calculations were used to thoroughly analyse the structural stability, electrical properties, optical features and thermoelectric capabilities of Ba₂XIO₆. The findings indicate that Ba₂XIO₆ (X = Li, K, and Rb) is crystallized in a resilient cubic double perovskite structure. The tolerance factors for Ba₂LiIO₆, Ba₂KIO₆, and Ba₂RbIO₆ are calculated to be 0.95, 0.86, and 0.86, respectively, supporting their structural stability. Electronic structure calculations reveal that Ba₂XIO₆ compounds are direct bandgap semiconductors with bandgaps located at the Γ point of the Brillouin zone. The computed bandgap values are 2.027&#xa0;eV for Ba₂LiIO₆, 2.016&#xa0;eV for Ba₂KIO₆, and 1.85&#xa0;eV for Ba₂RbIO₆. For the energy range of 0–13.5&#xa0;eV, real and imaginary portions of the dielectric function, absorption coefficient, optical conductivity, refractive index, reflectivity and energy loss function were all examined in a thorough analysis of optical characteristics using the OPTIC code. First peak reflectivity values were found to be 12%, 15%, and 21% for Ba₂LiIO₆, Ba₂KIO₆, and Ba₂RbIO₆, respectively. Furthermore, the thermoelectric performance was assessed using the BoltzTraP code, calculating the Seebeck coefficient, electrical conductivity, and thermal conductivity. The results indicate promising thermoelectric performance with a figure of merit (ZT) of 0.794, 0.808, and 0.793 for Ba₂LiIO₆, Ba₂KIO₆, and Ba₂RbIO₆, respectively. In summary, this first-principles study highlights the potential applications of Ba₂XIO₆ (X = Li, K, and Rb) in thermoelectric generators and optoelectronic devices, offering valuable insights into their multifunctional properties.</p>