A new quinazoline functionalized benzimidazole-based fluorogenic chemosensor H3L is synthesized and fully characterized by conventional techniques including single crystal X-ray analysis. It acts as a highly selective colorimetric and fluorescence sensor for Cu2+ ions in DMF/0.02 M HEPES (1 : 1, v/v, pH = 7.4) medium. Reaction of H3L with CuCl2 forms a mononuclear copper(II) [Cu(Cl)(H2L)(H2O)] (H2L–Cu2+) complex which is characterized by conventional techniques and quantum chemical calculations. Electronic absorption and fluorescence titration studies of H3L with different metal cations show a distinctive recognition only towards Cu2+ ions even in the presence of other commonly coexisting ions such as Li+, Na+, K+, Mg2+, Ca2+, Fe2+, Fe3+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+ and Hg2+. Moreover, H2L–Cu2+ acts as a metal based highly selective and sensitive chemosensor for S2− ions even in the presence of other commonly coexisting anions such as F−, Cl−, Br−, I−, SO42−, SCN−, AcO−, H2PO4−, PO43−, NO3−, ClO4−, NO2−, HSO4−, HSO42−, S2O32−, S2O82−, CN−, CO32− and HCO3− in DMF/0.02 M HEPES (1 : 1, v/v, pH = 7.4) medium. Quantification analysis indicates that these receptors, H3L and H2L–Cu2+, can detect the presence of Cu2+ and S2− ions at very low concentrations of 1.6 × 10−9 M and 5.2 × 10−6 M, respectively. The propensity of H3L as a bio-imaging fluorescent probe for detection of Cu2+ ions and sequential detection of S2− ions by H2L–Cu2+ in Dalton lymphoma (DL) cancer cells is also shown.