Novel electrochemical sensor based on poly(p-coumaric acid) electrodeposited on the surface of multi-walled carbon nanotubes modified glassy carbon electrode (poly(p-coumaric acid)/MWNT/GCE) has been developed for the direct determination of l-cysteine. Poly(p-coumaric acid) has been obtained by potentiodynamic electrolysis under the optimized conditions (0.10 mM p-coumaric acid in 0.1 M NaOH using 5 cycles in the potential window of 0–1.0 V and the scan rate of 25 mV s⁻¹) providing highest voltammetric response of l-cysteine. Sensor surface has been studied by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The porous structure of polymeric film provides 6.9-fold increase in effective surface area and 4.2-fold lower charge transfer resistance in comparison to GCE. Under conditions of DPV, the sensor response is linear in the ranges of 7.5–50 and 50–1000 μM of l-cysteine with the detection and quantification limits of 1.1 and 3.6 μM, respectively. The excellent sensor selectivity to l-cysteine in the presence of glucose, uric and ascorbic acids, dopamine, l-tyrosine and S-containing substances (homocysteine, glutathione, l-methionine, l-cystine and α-lipoic acid) has been observed. Applicability of the sensor to real samples analysis has been shown on example of human urine.