The first manganese member in a Pb-M-In-Q system, PbMnIn2S5, has been discovered by a high-temperature solid-state reaction. It adopts a Sr2Tl2O5 structure type in orthorhombic space group Cmcm (No. 63) with a = 3.896(2) angstrom, b = 12.731(7) angstrom, c = 15.770(9) angstrom, and Z = 1. The structure consists of corrugated layers made by (In1/Mn1)S-6 octahedra that are further interconnected by chains of edge-sharing (In2/Mn2)S-6 octahedra into a three-dimensional framework; Pb2+ cations are coordinated in PbS8 bicapped triangular prisms that are face-shared along the a direction. The crystallographically distinguished octahedrally coordinated 8f and 4b sites are disordered by Mn and In atoms. Such a structure allows antiferromagnetic interactions between the high-spin Mn2+ anions. The optical band gap is measured to be about 1.45 eV.