The fascinating characteristics of one-dimensional van der Waals crystals (V–VI–VII) enable their wide functionality. In particular, their anisotropic carrier transport and low thermal conductivity are advantageous from a thermoelectric viewpoint. In a quest for the “electron crystal phonon glass” paradigm, the present work investigated the thermoelectric performance of BiSBr. Deep insights were gained into the structural and electronic properties that revealed the synergetic effect of the bonding heterogeneity, lone pair of electrons, and degenerated bands that accelerated favorable transportation. Consequently, a low lattice thermal conductivity (0.225 W m⁻¹ K⁻¹) and considerable power factor (3.471 mW m⁻¹ K⁻²) and thus a high zT of 2.34 were noted in the x-direction (perpendicular to the chain) at 500 K in the case of the material with 1.5 × 10²⁰ holes per cm³. These observations suggest that BiSBr is a plausible near-room-temperature anisotropic thermoelectric mineral.