Lacosamide is a third-generation anticonvulsant used in the treatment of epilepsy. While therapeutic levels for various patient subpopulations are still under investigation to achieve optimal responses, therapeutic drug monitoring has been proven to be useful in improving patient management. To ensure the reliability of results, it is essential to establish a reliable quantitative method. Thus, the aim of this study was to develop and validate a simple and feasible method for quantifying lacosamide in human plasma, with the specific aim of facilitating drug monitoring purposes. A high-performance liquid chromatography method with ultraviolet detection was developed for the quantification of lacosamide in human plasma. Analyte recovery was achieved through ethyl acetate extraction, with propranolol serving as the internal standard. A C18 column and a mobile phase consisting of 10 mM phosphate buffer and acetonitrile (70:30 v/v, pH = 3.5) were employed. Validation parameters included specificity, linearity, repeatability, precision, accuracy, sensitivity, and stability. The method exhibited linearity within the range of 2.5 – 30 μg/ml (R² = 0.997), with a limit of quantitation of 2.29 μg/ml. The average recovery percentage was 100.2%, and it proved to be accurate, precise, and specific. In plasma samples, the drug content remained stable for 72 h at 4°C, 1 month at −20°C, and 2 years at −80°C. The post-processed sample remained stable for 1 week under all tested conditions. Due to its simplicity, short analysis time, sensitivity, and cost-effectiveness, the proposed analytical method proves to be useful for therapeutic monitoring and pharmacokinetic studies of lacosamide.