Currently, the novel combination of double perovskites Na2ScCuX6 (X = Cl, Br) is being investigated as a potential solution to fulfil the energy requirements. For this purpose, the stability, vibrational, mechanical, electro-optic, and transport properties are addressed systematically. The tolerance factor and Born mechanical criteria ensure structural and mechanical stabilities. The calculated formation and Gibbs free energies ensure the thermal stabilities. Thermodynamic properties against temperature and pressure are explored by discussing entropy, thermal expansion, and Debye temperature. The elastic characteristics have provided insight into anisotropy and mechanical strength. Meanwhile, ductile nature is characterized by the Poisson ratio and Pugh's ratio. The electronic aspects have estimated the band gaps of Na2ScCuCl6 and Na2ScCuBr6, which yielded values of 1.63 and 1.58 eV, respectively. The materials demonstrated substantial light absorption (order of 105 cm−1) and minimal reflectivity (below 25 %) in the visible range. The thermoelectric performance has been evaluated in the temperature range of 100–600K using the Seebeck effect, conductivities, and figure of merit. Lastly, the superior figure of merit (ZT) values ranging between 0.78 and 0.84 demonstrate the suitability of materials for thermal energy conversion. Therefore, Na2ScCuCl6 and Na2ScCuBr6 have the potential to be considered feasible candidates for energy harvesting applications.