In the title mol-ecule, C(21)H(15)ClN(4)S, the triazoloisoquinoline ring system is approximately planar, with an r.m.s. deviation of 0.054 (2) Å and a maximum deviation of 0.098 (2) Å from the mean plane for the triazole ring C atom that is bonded to the thia-zole ring. The thia-zole and benzene rings are twisted by 66.36 (7) and 56.32 (7)°, respectively, with respect to the mean plane of the triazoloisoquinoline ring system. In the crystal structure, mol-ecules are linked by inter-molecular C-H⋯N inter-actions along the a axis. The mol-ecular conformation is stabilized by a weak intra-molecular π-π inter-action involving the thia-zole and benzene rings, with a centroid-centroid distance of 3.6546 (11) Å. In addition, two other intermolecular π-π stacking inter-actions are observed, between the triazole and benzene rings and between the dihydro-pyridine and benzene rings [centroid-centroid distances = 3.6489 (11) and 3.5967 (10) Å, respectively].