The breadth and depth of applications for two-dimensional (2D) materials which, by their nature, are nanoscale and layer structured with a high surface to volume ratio, are extensive and rapidly transforming the field of gas sensing. Facile preparation methods, as well as novel electronic and surface properties that enable functionalisation, provide high sensitivity for gases commonly encountered in natural and industrial environments. Gas sensors that are operational at room temperature offer low power demand and thermal safety during analysis. This review focuses on room-temperature gas sensing performance of conductometric devices employing 2D hybrid nanomaterials including layered transition metal dichalcogenides (TMDs) and graphene materials. The effect of hybridisation of 2D nanomaterials on gas sensing performance and their sensing mechanisms are studied. Hybrid forms of 2D materials occur by the addition of metals, or polymers to surface sites, or by combining two or more different materials (i.e. nanocomposites) or by developing a heterojunction layer, which lead to enhanced collective performance. Gas sensing mechanisms depend on the type and format of 2D material but fundamentally involve gas adsorption on an active surface with a resultant change in the resistive property of the material.