In this article, we have systematically investigated the structural, electronic, optical and thermoelectric properties of Rb2Ag(Ga/In)Br6. The resulting negative formation energy along with the absence of imaginary phonon modes confirm the thermodynamic stability of Rb2Ag(Ga/In)Br6. In addition, the derived electronic properties by using GGA-PBE + mBJ + SOC functional show that the direct band gap values are 1.21 eV and 1.42 eV for Rb2AgGaBr6 and Rb2AgInBr6, respectively. Furthermore, the dispersed direct band nature of Rb2Ag(Ga/In)Br6 leads to their outshining optical properties such as higher order (105 cm−1) absorption coefficient, appreciable optical conductivity, and low reflectivity. Moreover, the higher figure of merit values of Rb2Ag(Ga/In)Br6 are resulted from their ultra-low thermal conductivity and high electrical conductivity. Thus, Rb2Ag(Ga/In)Br6 are predicted to be potential photovoltaic and thermoelectric materials.