<p>This article discusses the development of a novel electrochemical sensor and highlights the benefits of utilizing the electrochemical method for precise monitoring of the thyroid hormone, T₄. The sensor functions through electrochemical interactions between the T₄ molecule and the electrode surface, which includes N-ethyl-2-picolinoylhydrazine carbothioamide, EPHC. By using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy, the sensor delivered dependable and precise results, with prospective applications in free-T₄ monitoring. EPHC was synthesized and characterized using furrier transform infrared spectroscopy, scanning electron microscope, and energy dispersive X-ray spectroscopy techniques to confirm successful synthesis. EPHC was blended with suitable components to formulate a consistent carbon paste, to which a graphite bare was affixed for electrical connectivity. The sensor demonstrated impressive performance, achieving a low detection limit of 8.0 × 10⁻³ µM. It operated effectively across a linear range from 8.7 × 10⁻³ to 80.0 µM. The response time was rapid at 30&#xa0;s. The electrode exhibited satisfactory repeatability and reproducibility. The sensitivity for T₄ was measured at 1.17 µA µM⁻¹, reflecting the sensor’s strong analytical capability. The sensor successfully quantified free-T₄ in different real matrices, under optimized conditions of a pH of 9, a scan rate of 80 mV s⁻¹, 5.0&#xa0;mg of EPHC, and 0.5&#xa0;g of graphite powder.</p> Graphical Abstract <p></p>