In the title compound, C(15)H(12)N(4)OS, the dihedral angle between the nine-membered indolin-2-one ring system and the phenyl ring is 2.72 (7)°. Intra-molecular cyclic N-H⋯O and C-H⋯S hydrogen-bonding inter-actions [graph set S(6)] are present, as are weak N-H⋯N inter-actions [graph set S(5)]. In the crystal, mol-ecules form centrosymmetric cyclic dimers through pairs of N-H⋯O hydrogen bonds [graph set R(2) (2)(8)] and these are extended by C-H⋯S inter-actions. The crystal structure also features weak C-H⋯π inter-actions.