Psidium guajava extract is sold as a dietary supplement for delaying the onset of various diseases. It has been reported to have exemplary antioxidant properties. Herein we report an electrochemical sensor for the detection of Morin (MR) for the first time in Psidium guajava leaf extract which has been reported to have MR. Nickel (II) phthalocyanine (NiPc) complex is used in the surface modification of the carbon paste electrode (CPE) by bulk modification method and characterized by spectroscopic techniques. Combining the favorable properties of NiPc and CPE assembles into a formidable sensor for facile quantification of biomolecules. We observed a significant electroactivity at the modified electrode with a notable twelvefold enhancement in anodic peak current at physiological pH. A wide linear dynamic range of 2.5 × 10 −3 to 1.0 × 10 −7 M, with a limit of quantification and limit of detection achieved, was 6.9 nM and 2.0 nM (S/N = 3) respectively. The proposed sensor could resolve the peaks of quercetin and morin effortlessly and simultaneously. The proposed biosensor is swift, simple to fabricate, with low limits of detection and remarkable antifouling properties. The sensor was used in the validation of spiked red wine, human urine, tea decoction and commercially available guava leaf capsules, with satisfactory recoveries.