This study focused on the synthesis, photocatalytic degradation of organic dyes and biological activity of novel N, N, O-donor tridentate water soluble 4-hydroxy benzohydrazide-grafted biopolymer Schiff base Cu(II) complexes. The eco-friendly catalysts were designed for potential application in the degradation of organic dyes. The photocatalytic degradation of methylene blue was investigated with various irradiation times (30, 60, 90 and 120 min), catalytic dosages (5, 10, 15 and 20 mg) and pH (3, 7 and 12). The as-prepared compounds were characterised via various techniques including FT-IR and FT-NMR spectroscopy; TGA-DTA, XRD, SEM-EDAX; ESR and UV-vis spectroscopy; photoluminescence, magnetic moment, and conductivity measurements; and elemental and thermal analysis. The crystallinity of the Schiff base ligands, chitosan, and their Cu(II) complexes was analysed via X-ray diffraction (XRD) studies. The XRD patterns revealed that the polymer chitosan was more crystalline than the Schiff base ligands and their complexes. The surface morphological analysis by scanning electron microscopy (SEM) revealed that the Cu(II) complexes were amorphous in nature compared to chitosan and the ligands. The anti-inflammatory and anti-diabetic studies of the biopolymer Cu(II) complexes were performed using the albumin denaturation technique and McCue and Shetty method, respectively. The as-synthesized 4-hydroxy benzohydrazide-grafted O-carboxymethyl chitosan Schiff base ligands and their Cu(II) complexes showed a good anti-inflammatory and antidiabetic effect. The photocatalytic activity proved that the aryl-substituted complex was more efficient than the aliphatic-substituted complex.