The mol-ecule of the title compound, C(16)H(9)ClN(2)OS, is approximately planar, the dihedral angle between the thia-zolo[3,2-a]benzimidazole ring system and the 4-chloro-phenyl ring being 2.10 (5)°. An intra-molecular C-H⋯S inter-action generates an S(6) ring motif. In the crystal, mol-ecules are stacked into columns along the b axis by π-π inter-actions with centroid-centroid distances of 3.6495 (7)-3.9546 (8) Å.