This report demonstrates the sustainable synthesis of hybrid biopolymer hydrogel supported Au NPs followed by its characterizations and biological explorations. The chitosan/pectin (CS-Pec) composite hydrogel was used as the support. The biopolymers might function as an eco-friendly reductant for the Au3+ ions over and above encapsulating stabilizer of the Au NPs by exploiting their electron rich organo-functions. UV–Vis, SEM, TEM, EDX, elemental mapping and XRD techniques were engaged to appraise the physicochemical features of the material. Subsequently, the material (Au NPs@CS-Pec) was subjected to diverse biological applications and following the course it showed high antioxidant activities against DPPH free radical. The related IC50 of the antioxidant material against DPPH found as 139 µg/mL. Towards the oncological investigation, it was used against the gastric cancer cell lines (AGS and KATO III) and the corresponding IC50 values were 225.3 and 341.5 µg/mL respectively. The outcome justifies that the produced NPs have successfully inhibited the proliferation of gastric cancer cells, and those are mostly eliminated at a high dose of the NPs.