3-Ethoxysalicylaldehyde S-allylisothiosemicarbazone hydrobromide, HL a new tridentate Schiff base and its cationic complexes of Co[1], Ni[1], Cu[1] and Zn[1] were successfully prepared. The typical formulae for complexes are [Co(L)2](1), [Ni(L)2](2), [Cu(L)2](3) and [Zn(L)2](4). The prepared complex analogues have been characterized with instruments such as infrared, 1H NMR, 13C NMR, elemental analysis, electronic and fluorescence spectroscopic studies. The physicochemical results showed that the Schiff base (HL) coordinates the NNO donor set to form tridentate to the central metal ions. Although complexes of the HL ligand exhibited significant fluorescence intensity. The synthesized compounds have been tested against bacterial pathogens. Compared to the reference antibiotic drug, streptomycin, the [Zn(L)2] complex was very effective against both microorganisms in the zone of inhibition ranges (22–27 mm) and (28–30 mm). Additionally, the anti-diabetic qualities were also looked into. When compared to the reference drug acarbose, which has an IC50 = 33.17 ± 2.39 µm, the [Cu(L)2] and [Zn(L)2] complexes have inhibitory potential against α-amylase with significant inhibition of IC50 = 28.37 ± 2.17 and 29.53 ± 2.08 µm. The desired ligand-protein interactions with the active site residues were suggested by the molecular docking studies. Whereas the [Ni(L)2] and [Zn(L)2] complex shown well-oriented interaction conformations with a -6.5 kcal/mol for E. coli (PDBID: HNJ) protein active site. Hydrogen, hydrophobic, and electrostatic bonds interactions were also generated by some of these complexes. In-silico analysis of the ADME properties of the bioactive HL ligand have been shown that drug-likeness property