In the title compound, C18H19N3S, the dihedral angle between the planes of the benzene rings is 58.63 (8)degrees. The six-membered ring bonded to the thiosemicarbazide group (r.m.s. deviation = 0.038 angstrom) adopts a sofa conformation, with one of the methylene-group C atoms as the flap. A short intramolecular N-H center dot center dot center dot N contact is observed. In the crystal, molecules are linked by weak N-H center dot center dot center dot S interactions to generate C(4) chains propagating in the  direction, with adjacent molecules related by glide symmetry.