Early diagnosis of lung cancer has gained much attention in the last few years due to its high incidence and fatality rate. In this paper, Sc-doped SnS2 (Sc − SnS2) monolayer is proposed as a promising biosensor to diagnose lung cancer in the early stage. Employing DFT-based investigation, the adsorption mechanism of three prominent biomarkers C3H4O, C3H6O, and C5H8 in the exhaled breath of lung cancer patients is analyzed. The effect of Sc-doping on pristine SnS2 is studied first followed by an investigation of the adsorption mechanism via. structural, magnetic, and electronic properties. Based on binding energy calculations, a single Sc atom adsorbs on the Sn-site of the SnS2 surface and is chosen as a molecular model for adsorption analysis. The findings revealed that the Sc-SnS2 monolayer had exceptional adsorption ability for three common volatile organic compounds (VOCs) found in lung cancer patients, resulting in a significant change in the physicochemical parameters of the sensing Sc-SnS2 system. The results projected Sc − SnS2 monolayer as a promising biosensor to diagnose lung cancer at an early stage and provide a way for experimentalists to explore it in the real application. Moreever, the charge-transfer behavior under the effect of electric field is also examined in order to explicate the expediency of Sc-doped SnS2 monolayer as a field-effect-transistor sensor.