This study investigates dynamic subcritical water extraction (SWE) as a novel, single-step, and environmentally sustainable method for the recovery of allicin from Allium sativum L. Unlike conventional extraction techniques, SWE extracts allicin and hydrolyse alliin simultaneously within a closed system, eliminating the need for organic solvents. Response Surface Methodology (RSM) was employed to optimize temperature (120–180 °C), flow rate (2–6 mL/min), and extraction time (10–30 min). The optimal conditions of 150 °C, 4 mL/min, and 30 min produced the highest allicin concentration (2.548 mg/g_sample) and extract yield (1.695 g). Solubility analysis revealed maximum values for extract yield (0.045 g/mL), alliin (6.841 mg·mL/g_sample), and allicin (0.082 mg·mL/g_sample), highlighting the influence of solvent polarity and mass transfer efficiency under subcritical conditions. Kinetic modelling using the Esquivel and Brunner models, selected as empirical and diffusion-based approaches commonly applied to solid–liquid extraction systems, showed excellent correlation (R² = 0.984–0.999), confirming diffusion-controlled extraction behaviour, with the Brunner model demonstrating superior predictive accuracy. SWE efficiently unifies hydrolysis and extraction within a single, eco-friendly, and scalable system, enabling effective recovery of allicin and other bioactive compounds.