The 2D monolayer of transition metal carbo-dichalcogenide (TMCC) has been recently synthesized from its bulk form. It is a unique blend of MXenes and transition metal dichalcogenides (TMDCs), offering superior properties compared to its individual parent components. TMCC has not yet been explored for its potential in gas sensing applications, motivating us to investigate its performance for detecting H2S gas molecule. The pristine monolayer of TMCC (Nb2S2C) exhibited weak H2S adsorption energy (-0.18eV), leading to low sensitivity, poor selectivity, underscoring surface modification. The decoration strategy was incorporated by considering transition metal (TM) atoms like Ti, Co, Cu, Pd and Ag. Ti and Co decorated TMCC showed superior H2S gas sensing performance. Ti showed maximum binding energy (-5.44eV) followed by Co (-4.91eV). The adsorption energy of H2S on Ti and Co decorated TMCC were comparable having values of -1.08eV and -1.09eV respectively while showing respective practical recovery time of 6s and 8.5s at 350K, respectively. The improved adsorption mechanism is due to orbital interaction and charge transfer. Work function sensitivity and thermal stability upto 400K was assessed. The study shows Ti and Co decorated TMCC monolayer as a suitable candidate for H2S sensing, inspiring experimentalists to fabricate TMCC-based H2S sensors.