Herein, the optoelectronic, structural, thermoelectric and elastic features of halide double perovskites (HDPs) Cs₂XInCl₆(X=Ag, Na) are examined by using full‐potential linearized augmented plane wave (FP‐LAPW) technique. The Generalized Gradient Approximation (GGA) and Tran‐Blaha modified Becke‐Johnson (TB‐mBJ) potential is employed to figure out the features of mentioned compounds. The computed values of direct band‐gaps (E_g) for Cs₂AgInCl₆ and Cs₂NaInCl₆ compounds are 2.52 and 5.24 eV, correspondingly. The stability of perovskites is confirmed in terms of formation energy ΔH_f, tolerance factor (τ) and octahedral factor. Furthermore, optical properties analysis demonstrates that studied compound exhibit conductivity and absorptivity across a broad range of incident photon energy with minimum R(ω). Moreover, outcomes of elastic parameters display isotropic and ductile nature for both materials. Thermoelectric (TE) properties like thermal conductivity (k/τ), power factor (PF), electrical conductivity (σ/τ) and Seebeck coefficient (S) are also calculated by utilizing BoltzTrap code. Cs₂NaInCl₆ attained the maximum value of ZT (0.76) with PF of 0.42. Computed TE and optical parameters indicate that Cs₂XInCl₆(X=Ag, Na) are promising for usages in solar absorbing and energy conversion devices.This article is protected by copyright. All rights reserved.