Heavy metal ions in drinking water result from industrialization and can cause a nuisance to the environment. Due to their toxicity and carcinogenic tendencies toward humans, determining heavy metal ions remains challenging. This study focuses on creating a cutting-edge electrochemical sensor with unprecedented sensitivity to lead (Pb (II)). In present investigation, we have hydrothermally produced lanthanum porous coordination polymer (La-TMA), which was further modified with Cr nanoparticles, characterized with structural, morphological, electrochemical and spectroscopic techniques, and used as a sensing material. The differential pulse voltammogram pattern of the Cr@La-TMA sensor indicates an affinity for Pb(II). All sensing parameters have been investigated: sensitivity, selectivity, repeatability, reproducibility, and linearity. The Cr@La-TMA sensor shows selectivity towards Pb(II), which is validated by the interference study for various analytes such as Cd(II), Hg(II), Cu(II), Cr(II), and Fe(II). The sensor exhibited excellent linearity for the concentration range of 1 nM to 10 nM with a limit of detection of 1 nM, which is below the MCL level suggested by the US-EPA and WHO. Furthermore, Cr@La-TMA was also validated for tap water samples, which confirms the sensor's viability. The proposed sensor would be incredibly useful for the real-time monitoring of heavy metal ions.