In this paper, a Schiff base ligand 1-(2-thiophenylimino)-4-(N-dimethyl)benzene (SL₁) bearing azomethine (>C=N-) and thiol (-SH) moieties capable of coordinating to metals and forming colored metal complexes was synthesized and examined as a colorimetric chemosensor. The sensing ability toward the metal ions of Cu²⁺, Cr³⁺, Fe²⁺ Ni²⁺, Co²⁺, Mg²⁺, Zn²⁺, Fe²⁺, Fe³⁺, NH₄VO₃ (V⁵⁺), Mn²⁺, Hg²⁺, Pb²⁺, and Al³⁺ was investigated in a mixture of H₂O and dimethylformamide (DMF) solvent using the UV–Visible spectra monitoring method. The synthesized Schiff base ligand showed colorimetric properties with Cr³⁺, Fe²⁺, Fe³⁺, and Hg²⁺ ions, resulting in a different color change for each metal that could be identified easily with the naked eye. The UV–Vis spectra indicated a significant red shift (~69–288 nm) from the origin after the addition of the ligand to these metal ions, which may be due to ligand-to-metal charge-transfer (LMCT). On applying Job’s plot, it was indicated that the ligand binds to the metal ions in a 2:1 ligand-to-metal molar ratio. SL₁ behaves as a bidentate ligand and binds through the N atom of the imine group and the S atom of the thiol group. The results indicate that the SL₁ ligand is an appropriate coordination entity and can be developed for use as a chemosensor for the detection of Cr³⁺, Fe²⁺, Fe³⁺, and Hg²⁺ ions.