In this study, we employ first-principles density functional theory (DFT) to investigate the electronic, magnetic, and thermodynamic properties of niobium-decorated tungsten disulfide (Nb@WS2), a potential material for gas capture and sensing. The adsorption behavior of CO, HCHO, NO, and NO2 was systematically investigated. Adsorption energies (Eads) range from 1.481 eV (CO) to 3.290 eV (NO2), with NO2 exhibiting the strongest interaction due to the high difference in electronegativity between interacting N and Nb atoms. Partial density of states (PDOS), Bader charge analysis, electron density difference (EDD), and electron localization function (ELF) collectively reveal significant charge transfer from Nb@WS2 to gas molecules, confirming the chemisorption nature of the interactions and the emergence of distinct electronic and magnetic signatures. Work function analysis showed notable increases upon gas adsorption, correlating with sensitivity enhancements of up to 18.24 % for NO. However, the elevated Eads values observed in these systems, leading to their enormous recovery times, pose specific challenges for their practical use as reusable gas sensors. Moreover, ab initio molecular dynamics (AIMD) simulations at 500 K confirm the thermal stability of gas-adsorbed configurations, reinforcing the viability of Nb@WS2 for high-temperature sensing or capturing applications.