This work describes the electroanalytical determination of pendimethalin herbicide levels in natural waters, river sediment and baby food samples, based on the electro-reduction of herbicide on the hanging mercury drop electrode using square wave voltammetry (SWV). A number of experimental and voltammetric conditions were evaluated and the best responses were achieved in Britton–Robinson buffer solutions at pH 8.0, using a frequency of 500s⁻¹, a scan increment of 10mV and a square wave amplitude of 50mV. Under these conditions, the pendimethalin is reduced in an irreversible process, with two reduction peaks at −0.60V and −0.71V, using a Ag/AgCl reference system. Analytical curves were constructed and the detection limit values were calculated to be 7.79μgL⁻¹ and 4.88μgL⁻¹, for peak 1 and peak 2, respectively. The precision and accuracy were determinate as a function of experimental repeatability and reproducibility, which showed standard relative deviation values that were lower than 2% for both voltammetric peaks. The applicability of the proposed methodology was evaluated in natural water, river sediments and baby food samples. The calculated recovery efficiencies demonstrate that the proposed methodology is suitable for determining any contamination by pendimethalin in these samples. Additionally, adsorption isotherms were used to evaluate information about the behavior of pendimethalin in river sediment samples.