Herein, we have proposed a thiourea sensor using a novel silver decorated chitosan (Ag@CTSN) nanocomposite modified glassy carbon electrode (GCE). The catalyst was fabricated using a simple photo-reduction technique. In where, chitosan surface was decorated with silver nanoparticles via the photochemical reduction of silver salt to obtain Ag@CTSN nanocomposite. The morphology and structural properties of fabricated electrocatalyst was successfully characterized using advanced analytical techniques and reviled that silver nanoparticles was nicely dispersed over the host matrix; chitosan. Morphological study shown the non-aggregated form of silver nanoparticles with an average diameter of 20.85 nm. In the electrochemical investigations, the Ag@CTSN/GCE sensor showed good sensitivity of 15.88 µAmM−1 cm−2, a wide detection range (200–3600 µM), and a low limit of detection (LOD ~18 μM). The newly developed thiourea sensor was further used to check the potential chemical interference using several common chemicals, presenting an extreme selectivity in thiourea detection. The Ag@CTSN/GCE sensor also exhibited ⁓100% recovery results from spiked real samples. Excellent reproducibility, repeatability, and operational and storage stability was observed in the newly fabricated sensor.