In the title pyrimidine-2,4-dione derivative, C 14H 16N 2O 2S, the dihedral angle between the six-membered rings is 77.81 (10)°. The molecule is twisted about the C p—S (p = pyrimidine) bond, with a C—S—C—N torsion angle of −59.01 (17)°. An intramolecular C—H⋯S hydrogen bond generates an S(5) ring motif. In the crystal, bifurcated acceptor N—H⋯O and C—H⋯O hydrogen bonds generate inversion-related dimers incorporating R 2 1(9) and R 2 2(8) loops. These dimers are connected into a chain extending along the a-axis direction by a second pair of inversion-related N—H⋯O hydrogen bonds, forming another R 2 2(8) loop. The crystal structure is further stabilized by weak intermolecular C—H⋯π interactions, generating a three-dimensional network.