We present here the multitasking capabilities of Ag-embedded ZnO nanocomposites (Ag–ZnO NCs), which include the photocatalytic degradation of organic dyes, bacterial inhibition, and cancer therapeutics. Ag-embedded ZnO nanocomposites (Ag–ZnO NCs) of mesoporous spherical morphology (size ∼ 150 ± 50 nm) are successfully synthesized by a facile and single step soft-chemical approach. To understand the effect of Ag loading on multitasking properties, Ag–ZnO NCs are synthesized with different wt% of Ag. It was found that Ag₅-ZnO NCs (5 wt% of Ag) showed excellent solar light-induced photocatalytic degradation properties against both cationic as well as anionic dyes. In addition, the presence of Ag in these NCs makes them strongly antibacterial, and kills 100% Escherichia coli (E. coli) cells within 2 hours (under dark), and within 30 min (under solar light). The enhanced photocatalytic and antibacterial activity of Ag–ZnO NCs is due to the anchoring of Ag NPs onto ZnO as well as minor substitution of Ag ions in the lattice of ZnO. This produces abundant charge carriers and generates significantly enhanced reactive oxygen species (ROS), which seem responsible for the multitasking properties. Furthermore, the cytotoxic study shows that Ag₅-ZnO NCs kill oral carcinoma (KB) cells under visible light irradiation, and work as photosensitizers towards the photodynamic therapy of cancer due to the excellent photocatalytic activity. The high ROS concentration depolarizes the mitochondrial membrane potential, which in turn initiates apoptosis in oral carcinoma (KB) cells inducing cell death. Therefore, the as-prepared mesoporous Ag–ZnO NCs show great promise in waste water treatment, and cancer therapeutics.