Rb2AgBiX6 (X = Cl, Br, I) double perovskites have been studied theoretically using DFT (density functional theory) as implemented in the WIEN2k algorithm. These materials’ tuneable band gaps and intriguing electrical characteristics have drawn interest in light of their possible uses in optoelectronic systems. Both Rb2AgBiCl6, Rb2AgBiBr6 and Rb2AgBiI6 crystallise in a cubic perovskite structure, retaining stability and displaying minor differences in lattice parameters because of the substitution of halides, according to the structural study. Due to the halides differing electronegativity and atomic sizes, the electronic structure calculations reveal that these double perovskites have indirect band gaps, with the band gap energy dropping as the halide transitions from Cl to I. These materials are appropriate for photovoltaic and photodetector applications due to a notable absorption in the visible region, as revealed by optical property investigation. The potential of Rb2AgBiX6 double perovskites in next-generation optoelectronic devices is highlighted by the combination of these features.