In this work, a novel low-cost electrochemical sensor involving copper bismuthate (CuBi2O4) microspheres embedded in reduced graphene oxide (rGO) is described for electrochemical determination of L-Tyrosine (L-Tyr) and photocatalytic degradation of methylene blue (MB) in Parkinson’s disease treatment and industrial waste treatment, respectively. The rGO improves the electrocatalytic behaviours of CuBi2O4 and enhances the sensing performance of L-Tyr. At the optimized conditions, the nanocomposites show good long-term stability, reproducibility, and fast response with nanomolar detection (6.9 nM) at wide linear ranges of 83–1234 × 10− 9 M (R2 = 0.9964) towards L-Tyr. Further, the photocatalytic dye degradation within 30 min was studied in the presence of CuBi2O4/rGO catalysts. The synthesized CuBi2O4/rGO composite enhances the dye degradation rate and shows good sensitivity to detect the L-Tyrosine compared to CuBi2O4. The results suggest that the self-assembled three-dimensional CuBi2O4/rGO microsphere is an excellent material for the detection of biomolecules and the removal of organic dyes.