The escalating threat of heavy metal contamination in water sources necessitates the development of efficient and cost-effective detection methods. This study explores the possibility of nickel slag waste (NSW) as a sustainable electrode material for the electrochemical sensor of Pb²⁺ ions through cyclic voltammetry (CV) and square wave voltammetry (SWV). The composition and morphology of the SNW were characterized using X-ray Fluorescence (XRF) and Scanning Electron Microscopy Energy Dispersive X-ray Spectroscopy (SEM-EDX). The analysis revealed a complex composition dominated by silica (SiO₂), magnesium oxide (MgO), and iron (Fe) with significant amounts of other elements such as nickel (Ni), aluminum (Al₂O₃), and titanium dioxide (TiO₂). The presence of these elements contributes to the electrode's high conductivity, structural integrity, and catalytic activity, which are crucial for efficient electrochemical sensing. Optimal detection was achieved at pH 5 being the optimal condition for Pb²⁺ detection due to favorable speciation and surface chemistry. The Gr/SNW composite electrode exhibited high sensitivity, with a limit of detection (LOD) as low as 0.005 ppm, and demonstrated strong linearity in Pb²⁺ concentration measurements. Additionally, the electrode showed excellent repeatability in performance, with RSD value, which was found to be 0.09%. These findings suggest that nickel slag waste is a promising candidate for developing low-cost, efficient electrochemical sensors for heavy metal detection.