In the title compound, C18H16N4OS, prepared by the reaction of 4-(acridin-9-yl)-1,1-dimethylthiosemicarbazide with methyl bromoacetate, the acridine and thiazolidine ring systems are both non-planar and, because of steric requirements, almost perpendicular, with a dihedral angle between their planes of 99.69 (6) degrees. C-H...O and C-H...pi(arene) hydrogen bonds stabilize the crystal structure in the solid state.