In the molecule of the title compound, C16H13N3O2S, one hydrazinic nitrogen atom is essentially planar, but the other is slightly pyramidalized. The torsion angle about the hydrazinic bond is 66.44 (15)°. Both hydrazinic hydrogen atoms lie antiperiplanar to the oxygen of the adjacent carbonyl group. The molecular packing is a layer structure determined by two classical hydrogen bonds, N—H...O=C and N—H...Nthiazole. The space group is P1 with Z = 1, which is unusual for an achiral organic compound.