Abstract The structural, electronic, optical, elastic, and thermoelectric (TE) characteristics of Na₂YCuX₆ (X = Br, Cl) halide double-perovskites (HDPs) were investigated by using first principle approach within WIEN2K code. Perdew, Burke and Ernzerhof generalized-gradient approximation (PBEsol-GGA) with modified Becke-Johnson (mBJ) potential were used in the current investigations. Enthalpy of formation energies (E_f) determined for Na₂YCuBr₆ and Na₂YCuCl₆ were −2.29 and −1.955 eV, correspondingly which verify the stability of both compounds. Na₂YCuBr₆ is discovered to be semiconducting with indirect bandgap (E_g) of 2.492 and Na₂YCuCl₆ has direct E_g of 2.571 eV. Absorption coefficient shows largest values at 5.74 and 6.92 eV for Na₂YCuBr₆ and Na₂YCuCl₆, correspondingly, which lie in UV range. Pugh’s ratio (B/G) values were calculated as 2.00 and 4.62 for Na₂YCuCl₆ and Na₂YCuBr₆, correspondingly which ensure the ionic bond and ductile characteristics of the compounds. From the TE calculations, ZT shows maximum values of 0.74 and 0.73 for Na₂YCuBr₆ and Na₂YCuCl₆, respectively. Results showed that investigated materials are efficient candidates for optoelectronic and TE appliances.