<p>Tin selenide has gained significant interest due to its remarkable performance in converting energy and its highly tunable electronic and optical characteristics. The purpose of this study is to provide a theoretical investigation of the structural, electronic, elastic, optical and transport properties of SnSe in its orthorhombic and rocksalt phases employing density functional theory (DFT) within WIEN2k. Calculations are performed within the Perdew–Burke–Ernzerhof (PBE) scheme of generalized gradient approximation (GGA) and the Tran–Blaha modified Becke–Johnson (TB-mBJ) potentials excluding and including spin-orbit (SO) coupling. The measured lattice parameters are in close agreement with previously reported experimental and theoretical values. Electronic structure analysis indicates an indirect gap in its orthorhombic phase which decreases under SO coupling and a direct gap in its rocksalt phase which increases under SO coupling revealing phase-dependent band gap nature. Elastic constants calculated with IRelast confirm mechanical stability and enable derivation of additional elastic properties. SnSe in both phases exhibits strong IR–visible polarizability. In both the SO-excluded and SO-included calculations, the orthorhombic form of SnSe shows its highest absorption predominantly in the UV range whereas the rocksalt structure achieves its peak absorption from the visible into the UV region underscoring its potential for optoelectronic and solar-energy applications. The power factor per relaxation time increases with temperature for both SnSe phases, shows almost no SO effect in the rocksalt phase, displays a small SO-related enhancement in the orthorhombic phase-strongest for TB-mBJ with SO and remains higher in the orthorhombic structure highlighting its better thermoelectric efficiency.</p>