An appropriate conventional method has been utilised to synthesie new tridentate Schiff base ligand 4-chloro-2-((2,4-dihydroxybenzylidene)amino)benzoic acid with Co (II), Ni (II), Cu (II), and Zn (II) complexes. Several spectroscopic(FT-IR, 1H NMR, 13C NMR, UV–Vis, Mass), TGA-DTA, powder X-ray diffraction, and DFT calculations, were used to characterise these complexes. According to these spectroscopic investigations, the ligand coordinated with the metals via carboxylic oxygen, azomethine nitrogen, and hydroxyl oxygen, acting as a tridentate ligand. Appropriate geometry for every complex has been proposed based on spectroscopic and analytical data. In tetrahedral geometry with Co(II), Ni(II), Zn(II), and square planner with Cu(II) ion, the ligand functions as a tridentate via ONO donors. The optimal structure (bond length and bond angle) and chemical reactivity of the ligand and its metal complexes from their Frontier Molecular Orbitals (FMO) and Molecular electrostatic potential (MESP) calculations have been investigated using Density Functional Theory (DFT/B3LYP,6-31G**/6-311G**(d,p), and LanL2DZ basis sets) calculations. In vitro DPPH radical scavenging techniques were used to assess the antioxidant activity of the ligand and its metal complexes. The results indicated that all of the complexes exhibited good antioxidant activity, with the Cu (II) complex being the most potent with the lowest IC50 values. The ligand and complexes in vitro antibacterial activities were further explored by screening them against Gram(+ve) bacteria (Bacillus subtilis) and Gram(−ve) bacteria (E. coli). Significant activity was demonstrated by all synthesised compounds against the tested strains of bacteria. The antifungal activity of complexes against Aspergillus niger and Candida albicans was determined. The results indicated that Cu(II) complex exhibited good antifungal activity against Candida albicans, but not against Aspergillus niger. The fungal strain Aspergillus niger was not significantly inhibited by complexes. The complexes have greater antimicrobial activity than the Schiff base ligand, as indicated by the MIC values.