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The structural, electronic, optical, elastic, and thermoelectric (TE) characteristics of Na2YCuX6 (X=Br, Cl) halide double-perovskites 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 investigations. Enthalpy of formation energies determined for Na2YCuBr6 and Na2YCuCl6 were -2.29 eV and -1.955 eV, correspondingly which verify the stability of both compounds. It is found that Na2YCuCl6 has a semiconducting nature with direct bandgap (Eg) of 2.571 eV and Na2YCuBr6 has for indirect Eg of 2.492 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 , respectively which confirm the ductile nature and ionic bond in the compounds. From the thermoelectric calculations, ZT shows maximum values of 0.74 and 0.73 for Na2YCuBr6and Na2YCuCl6, respectively. Results showed that investigated compounds are efficient candidates for optical and TE applications.