Two-dimensional nanomaterials (2DNMs) have attracted significant research interest due to their outstanding structural properties, which include unique electrical nanostructures, large surface areas, and high surface reactivity. These adaptable materials have outstanding physicochemical characteristics, making them useful in a variety of applications such as gas-sensing, electronics, energy storage, and catalysis. Extensive research has been conducted in the pursuit of high-performance room-temperature (RT) gas sensors with good selectivity, high sensitivity, long-term stability, and rapid response/recovery kinetics. Metal oxides, transition metal chalcogenides, MXenes, graphene, phosphorene, and boron nitride have all been discovered as 2DNMs with strong potential for gas sensors. This review presents an in-depth analysis of current advances in 2DNM research. It includes synthetic techniques, structural stabilities, gas-sensing mechanisms, critical performance parameters, and factors influencing gas-sensing capabilities of 2DNMs. Furthermore, the present study emphasizes structural engineering and optimization methodologies that improve gas-sensing performance. It also highlights current challenges and outlines future research directions in the domain of tailoring 2DNMs for advanced RT gas sensors. This systematically designed comprehensive review article aims to provide readers with profound insights into gas detection, thereby inspiring the generation of innovative ideas to develop cutting-edge 2DNMs-based gas sensors.