In this work, we have successfully developed a novel amperometric sensor for the detection of Gallic Acid (GA) based on bismuth nanoparticles decorated multi-wall-carbon-nanotubes modified carbon paste electrode (Bi-MWCNT/MCPE) at physiological pH. We investigated electrochemical oxidation of GA at neutral pH since there is limited literature at this pH. Surface morphology of the synthesized Bi-MWCNT composite was examined using high resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD). Our fabricated Bi-MWCNT/MCPE was characterized with the aid of field emission scanning electron microscopy (FE-SEM) coupled to energy dispersive X-ray (EDX). The electron impedance spectroscopy (EIS) was employed to study the electrode–electrolyte interface properties, which depicted least electron transfer at Bi-MWCNT/MCPE. During Cyclic voltammetric (CV) analysis of GA at Bi-MWCNT/MCPE, we observed a threefold enhancement in anodic peak current (Ipa) compared to bare CPE. Amperometric quantitative analysis implied proportionality between Ipa and GA concentration in the range 1.0 to 100.0 μM with the lower detection limit (LOD) of 1.6 × 10−7 M (S/N = 3.3). Results from the interference study indicated good anti-interference property of the proposed sensor and could as well be subjected for real sample analysis, which was fortifying with GA. From the acceptable recoveries obtained we confirm the sensor’s practical applicability. Finally, the developed sensor offered many benefits such as excellent detection particularly at neutral pH, wide linear dynamic range, selectivity, stability, and reproducibility.