Herein, we report a highly sensitive, selective and simple electrochemical sensor for the detection of Zn2+ ions in less than 1 nM concentration range in aqueous environment. A naturally occurring and frequently cultivated Tricholoma mushroom polysaccharide is used for the preparation of novel sensor. In the present investigation we demonstrate an electrochemical sensor, grafted Tricholoma mushroom polysaccharide-based silver composite nanoparticles (TMPSGP-Ag NPs) which show remarkable electrochemical sensing performance of Zn2+ ions without interfering with the other relevant metal ions. The sensing performance is carried out by cyclic voltammetry (CV) and chronoamperometry (CA) analysis under optimised condition. The limit of detection (LOD) is found to be 0.53 nM, which is much lower than some other reported works as well as lower than the limit of World Health Organization (WHO). The stability, reproducibility and repeatability properties of the sensor are examined where a satisfactory result is obtained. The practical application of the proposed sensor is tested by the detection of Zn2+ ions using river water sample with an excellent performance. Therefore, the developed sensor can be used as a highly efficient and effective Zn2+ ions detector in aqueous medium.