<p>In this work, pristine and Ag-modified lanthanum succinate polymeric composites were prepared as selective electrochemical sensors for the monitoring of mercury (Hg²⁺) in aqueous media. Furthermore, Ag-modified La-succinate sensor effectively distinguished Hg²⁺ ions from potentially disruptive metal species. It has <i>R</i>² = 0.995 and a Freundlich adsorption capacity of 2.3&#xa0;mg/g. The measurements of electrochemical impedance were also employed to evaluate resistance due to charge transfer. The sensitivity of the sensor is optimized for the lowest concentration of Hg²⁺ ions in the aqueous media with limit of detection (LOD) of 0.1&#xa0;nM. The reported LOD for Hg²⁺ ions is well below the prescribed limit for the drinking water as per the World Health Organization. The reliability of this sensor was confirmed by evaluating its sensitivity (4.4 μAM⁻¹) and its selectivity for Hg²⁺ ions. In addition to this, the sensor has very good electrochemical stability and repeatability for the repeated exposures of the same concentration of Hg²⁺ ions. These notable parameters of Ag-modified La-succinate electrochemical sensor show its potential for detecting hazardous Hg²⁺ ions.</p> Graphical Abstract <p></p>