Metribuzin is a widely used pesticide with a half-life of up to 2 months and high affinity to organic matter that should be carefully monitored. Here is reported the development of a modified carbon paste electrode using cobalt phthalocyanine as a biomimetic catalyst for the determination of metribuzin. The diffusion coefficient of metribuzin at room temperature was (59 ± 16) × 10−6 cm2 s−1 and the apparent Michaelis–Menten constant (KapM) was (7.4 ± 0.6) × 10−6 mol L−1. Electroanalytical measurements were performed by amperometry and the following figures of merit were obtained: limit of detection of 5.3 × 10−6 mol L−1 (1.14 mg L−1), linear range up to 2.0 × 10−4 mol L−1, recoveries above 93% (performed on spiked water samples), interday repeatability of 4.5% and intraday repeatability of 3.5%, and suitable selectivity.