We report the structural, electronic, optical and thermoelectric properties of half-Heusler compound RbScSn within density functional theory (DFT) as implemented in Wien2k and semi-classical Boltzmann transport theory. The Tran-Blaha modified Becke-Johnson (TB-mBJ) potential is adopted to compute accurately the band gap of compound. The optimized lattice constant, bulk modulus and its pressure derivative within GGA and TB-mBJ approaches are reported. For both approximations, the alloy is found to be nonmagnetic semiconductor. Compared to the GGA approach, the TB-mBJ approximation has significantly improved the Gap value by a rate approaching 100%. Electronic calculations show that the RbScSn half-Heusler is an indirect bandgap semiconductor. The computation for elastic constants and mechanical parameters are done to check the mechanical stability, which revealed that the RbScSn is stable with ductile nature and low rigidity. The optical properties such as real and imaginary part of dielectric function, reflectivity, absorption coefficient and refractive index show interesting results. The high absorption coefficient of 11,382 x 10(4) cm(-1), registered at ultraviolet region accompanied by a high reflectivity of 64% observed in near infrared region, indicates the high potential of RbScSn compound to optical applications. Due to the narrow band gap semiconducting nature, the thermoelectric parameters are also calculated. A high merit factor close to unity was registered at room temperature. Based on the obtained results we can predicted that the RbScSn semiconductor is well suitable for some optical and thermoelectric applications.