<p>This study presents a physics-based multiphysics numerical model for the electrochemical sensing of niclosamide at a glassy carbon electrode modified with a multi-walled carbon nanotube/cyclodextrin (MWCNT/CD) nanocomposite. The proposed model integrates mass transport, charge conservation, and interfacial electrochemical kinetics within a porous electrode framework by coupling the Nernst–Planck transport equations, charge conservation in the solid and electrolyte phases, and Butler–Volmer reaction kinetics. Unlike conventional equivalent-circuit and simplified reaction–diffusion models, the developed framework provides a direct relationship between nanocomposite structural properties and electrochemical performance. A two-dimensional axisymmetric COMSOL Multiphysics model was developed while accounting for the porosity, tortuosity, effective conductivity, and internal surface area of the MWCNT/CD layer. Finite element simulations were performed to investigate the influence of nanocomposite thickness, diffusion behavior, and charge transfer resistance on the overall sensor response. The results demonstrate that the MWCNT/CD hybrid structure substantially improves electron transport pathways, increases the effective electroactive surface area, and enhances niclosamide detection sensitivity. In addition, optimization of the porous layer properties was found to alleviate kinetic limitations and improve the electrochemical performance of the sensor. The proposed model provides mechanistic insight into the sensing process and offers a predictive framework for the rational design of advanced nanostructured electrochemical sensors.</p>