There has been budding demand for the fast, reliable, inexpensive, non-invasive, sensitive, and compact sensors with low power consumption in various fields, such as defense, chemical sensing, healthcare, and safe environmental monitoring units. Particularly, efficient detection of chemical warfare agents (CWAs) is of great importance for human safety and security. Inspired by this, we explored molybdenum carbide MXenes (Mo2CTx; Tx = O, F, and S) as efficient sensors toward selected CWAs, such as arsine (AsH3), mustard gas (C4H8Cl2S), cyanogen chloride (NCCl), and phosgene (COCl2) both in aqueous and non-aqueous media. Our calculations based on van der Waals-corrected density functional theory (DFT) revealed that the CWAs bind with Mo2CF2, and Mo2CS2 monolayers under strong chemisorption with binding energies in the range of −2.33 to −4.05 eV, whereas Mo2CO2 resulted in comparatively weak bindings of −0.29 to −0.58 eV. We further reported the variations in the electronic properties, electrostatic potentials, and work functions of Mo2CTx upon the adsorption of CWAs, which authenticated an efficient sensing mechanism toward CWA detection. Statistical thermodynamic analysis was applied to explore the sensing properties of Mo2CTx at various temperatures and pressures. These findings will pave the way to an innovative class of low-cost reusable sensors for the sensitive and selective detection of highly toxic CWAs in air as well as in aqueous media.