Simple and highly sensitive voltammetric methods were developed using a poly(bromocresol purple) modified glassy carbon electrode to quantify cetirizine. Poly(bromocresol purple) film was synthesized on the surface of a glassy carbon electrode by cyclic voltammetry for 50 potential cycles in 0.1 M phosphate buffer at pH 6.0 containing 5.0 × 10−4 M of the monomer. Quantification of cetirizine exhibiting irreversible properties using the optimized conditions with a linear dependence between cetirizine concentration and peak currents from 0.2 to 100 µM for differential pulse voltammetry (DPV) and 0.1 to 100 µM for square wave voltammetry (SWV). Detection limits were 21.8 and 15.1 nM for DPV and SWV, respectively. Relative standard deviation (RSD) values below 0.98% indicated good precision. Recovery values from 100.12% to 100.90% with relative standard deviations below 1.14% for DPV and SWV in pharmaceutical formulations and urine samples demonstrated the high accuracy of the developed methods. The prepared modified electrode exhibited good fabrication reproducibility and suitable long-term stability. Finally, no interferences were observed in cetirizine determination in the presence of co-existing substances in the biological samples.