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Pb2+ ions are highly toxic to living beings because they tend to bioaccumulate in the body. For this reason, the development of simpler, low‐cost, and easy‐to‐operate techniques that can detect and quantify low concentrations of metal ions would help to identify contaminating media and improve public health. This work proposes a Pb2+ voltammetric sensor based on a carbon paste electrode modified with hydrothermal biochar (hydrochar, HC) obtained from malt bagasse waste (HC/CPE). The obtained hydrochar was characterized by zero‐charge point, FT‐IR, XRD and thermogravimetry. The differential pulse adsorptive anodic stripping voltammetry (DPAdASV) technique was used to perform the Pb2+ determination. After optimizing important parameters for detecting Pb2+ ions and the parameters of the voltammetric technique employed, a linear response range of 0.50 to 7.06 μmol L−1 with a limit of detection (LOD) and limit of quantification (LOQ) of 55.0 and 181.5 nmol L−1 were achieved, respectively. The developed voltammetric procedure was applied towards the Pb2+ determination at tap water and river water samples, with excellent recoveries (ranging of 91.19 to 109.22 %), proving that the HC‐based electrode has great potential for detecting Pb2+ ions. Hydrothermal carbonization allowed the biomass to be converted into functionalized hydrochar, eliminating the need for subsequent functionalization/activation steps for use as a Pb2+ adsorbing material on the electrodic surface. The proposed sensor also proved to be easy to assemble and environmentally friendly by using biomass waste as the carbon material. Thus, the proposed sensor adds to the literature the possibility of simple and easy detection of metal ions with a waste reuse bias. [ABSTRACT FROM AUTHOR]