Here,　we　investigate　PbSnS2,　a　wide　band　gap　(1.13　eV)　compound,　as　a　promising　thermoelectric　material　for　power　generation.　Single　crystal　X-ray　diffraction　analysis　reveals　its　2D-layered　structure,　akin　to　the　GeSe　structure　type,　with　Pb　and　Sn　atoms　sharing　the　same　crystallographic　site.　The　polycrystalline　PbSnS2　exhibits　an　intrinsically　ultralow　lattice　thermal　conductivity　(kappa(lat))　of　0.37　W　m(-1)　K-1　at　573　K.　However,　the　low　carrier　concentration　(n)　leads　to　suboptimal　electrical　conductivity　(sigma),　capping　the　ZT　value　at　0.1.　Accordingly,　the　halogen　elements　(Cl,　Br,　and　I)　are　employed　as　the　n-type　dopants　to　improve　the　n.　The　DFT　results　indicate　a　significant　weakening　of　Pb/Sn　&　horbar;S　bonds　upon　halogen-doping,　contributing　to　the　observed　reduction　in　kappa(lat).　Our　analysis　indicates　the　activation　of　multiconduction　band　transport　driven　by　halogen　substitution.　The　PbSnS1.96Br0.04　has　a　high　power　factor　of　five　times　that　of　intrinsic　PbSnS2.　Halogen-doping　weakens　the　Pb/Sn　&　horbar;S　bonds　and　enhances　the　phonon　scattering,　leading　to　an　ultralow　kappa(lat)　of　0.29　W　m(-1)　K-1　at　873　K　for　PbSnS1.96Br0.04.　Consequently,　PbSnS1.96Br0.04　achieved　a　maximum　ZT　value　of　0.82　at　873　K.