This study aimed to develop a novel electrochemical sensor using nano-gold particle modified pyrolytic graphite sheet electrodes to improve the detection and quantification of vitamin C content in sports beverages. The electrodes were fabricated by depositing 20–50 nm gold nanoparticles onto pretreated pyrolytic graphite sheets using a spontaneous adsorption technique. Square wave voltammetry served as the main analytical technique for optimizing and testing the performance of the nano-gold modified sensor. Key parameters optimized included supporting electrolyte pH, voltage scan rate and pulse frequency. The sensor gave highly linear detection across a vitamin C concentration range spanning 5–100 μg/mL, with sensitivity peaking under acidic pH 5 conditions. A limit of detection of 1.86 μg/mL was achieved. Recovery testing in spiked commercial sports drink samples yielded excellent accuracy between 97.3 and 104.2%. Additionally, vitamin C levels quantified via the sensor showed close agreement with results from a standard spectrophotometric method, confirming its reliability. This research signifies an important advancement in nutrient monitoring capabilities for the sports nutrition industry, providing a rapid, selective and cost-effective sensor for verifying vitamin contents.