Abstract In this paper, the first principle investigations are performed to compute the electronic, optical, magnetic and thermoelectric (TE) features of Ba_1−xMn_xS (x = 6.25%, 12.5% and 25%) alloys by using density functional theory (DFT). The semiconductor behavior of pure BaS and half metallic ferromagnetic (HMF) nature of Ba_1−xMn_xS (x = 6.25%, 12.5% and 25%) is confirmed by investigating electronic band structure (EBS) with spin-resolved density of states (DOS). The M_Tot is mainly originated from Mn atom due to the presence of 3d-orbitals. In addition, the optical constants including refractive index, absorption and optical spectrum, reflectivity and dielectric function are analyzed in the span of 0–10 eV. It is found that the studied alloy operate within visible to ultraviolet (UV) energy range. Moreover, the TE properties such as figure of merit (ZT), power factor (PF), electrical and thermal conductivity are also calculated by using the BoltzTrap package. The high values of ZTof Ba_1−xMn_xS (x = 6.25%, 12.5% and 25%) qualify it for use in TE applications.The outcomes revealed the application of Ba_1−xMn_xS in spintronic and TE gadgets.