Gallic acid (GA) is a natural phenolic compound with significant biological properties, including anti‐inflammatory, antioxidant, and anticancer effects. Detecting GA in biological matrices like food and beverages is essential but challenging due to the multitude of GA‐like molecules with similar proprieties and functional moieties. In this study, ultra‐small (≈4 nm) pyramidal platinum nanoparticles (PtNPs) with a high fraction of {111} surface domains are used to design a new electrochemical sensor for GA detection in tea, which is the most popular manufactured drink consumed in the world. PtNPs are deposited on a glassy carbon electrode (GCE) using a simple drop deposition method, requiring a minimal amount of nanoparticles and, hence, metal precursor. With just 2.7 µg of PtNPs, the sensor demonstrated a linear response in the concentration range from 50 to 600 µm, a detection limit of 16 µm, and a quantification limit of 49 µm. The sensor selectivity is tested against other antioxidant compounds commonly present in tea, consistently showing a higher response for GA. Furthermore, the sensor capability to detect GA in real green and black tea samples is further validated by high‐performance liquid chromatography (HPLC) analysis, with high correlation between chromatographic data and sensor response.