Spintronic technology and energy applications benefit greatly from the exceptional characteristics of rare-earth-based spinel chalcogenides. Examining the electrical, magnetic and thermoelectric properties of HgNd2Z4 (Z = S, Se) in a systematic manner is essential for the strategic advancement of spin polarized current in a spintronic device. In this recent study, the WIEN2K code was employed to comprehensively analyze these properties. The calculated lattice constants, obtained using the generalized gradient approximation (GGAsol-PBE), closely match experimental findings of the similar family compounds. The examination of the stability of ferromagnetic states in the ground state involves comparing energies between anti-ferromagnetic and ferromagnetic states. Moreover, an assessment of the stability of the cubic phase in both spinels was conducted using analyses of the phonon dispersion curve, formation energy and Born stability criteria. The ductility characteristics were examined through the calculation of Poisson's and Pugh's ratios. Furthermore, details regarding the density of states, spin polarization, exchange coupling and Curie temperature were provided to explore the characteristics associated with ferromagnetism. Potential optoelectronic applications were proposed, leveraging the direct band gaps of 1.4 and 1.0 eV for HgNd2Z4 (Z = S, Se) respectively, within the visible spectrum. Particularly noteworthy is the effective light absorption of HgNd2Se4 in the visible range, characterized by prominent peaks that facilitate the transition of electrons from the valence band (VB) to the conduction band (CB). Additionally, the study extends to thermoelectric characteristics, determining various factors such as Seebeck coefficient (S), figure of merit (ZT), electrical and thermal conductivities of the evaluated spinels.