<p>This study presents a comprehensive first-principles investigation of the structural, elastic, electronic, magnetic, optical, and thermoelectric properties of hexagonal ThX₅ compounds (X = Fe, Ni) using Density Functional Theory (DFT) within the GGA + U framework. The elastic constants and 3D mechanical property visualizations demonstrate strong anisotropy in ThFe₅, making it suitable for directional mechanical applications, while ThNi₅ displays more isotropic behavior, favoring uniform load-bearing roles. In addition, electronic structure analysis, including TDOS, PDOS, and band structures, confirms the metallic and magnetic nature of both materials, with ThFe₅ exhibiting stronger ferromagnetism due to higher magnetic moments and larger spin splitting. These magnetic features significantly influence transport and optical properties. The optical analysis, based on complex dielectric functions, reveals strong direction-dependent optical responses, with plasma frequencies and reflectivity spectra confirming metallic behavior in both compounds. Notably, ThFe₅ shows higher anisotropies in optical conductivity and extinction coefficients than ThNi₅. Furthermore, thermoelectric performance, evaluated using Boltzmann transport theory, exhibits distinct temperature-dependent behavior in the Seebeck coefficient, electrical conductivity, and power factor. ThFe₅ displays a complex spin-dependent thermoelectric response with a temperature-induced carrier-type crossover, while ThNi₅ shows a stable p-type dominance at higher temperatures.</p>