An energetic and dynamical stability analysis of five candidate structures—hexagonal, buckled hexagonal, litharge, inverted litharge, and distorted-NaCl—of the SnS monolayer is performed using density functional theory. The most stable is found to be a highly distorted-NaCl-type structure. The thermoelectric properties of this monolayer are then calculated using the density functional theory and the Boltzmann transport equation. In terms of phonon scattering, there is a sharp contrast between this monolayer and bulk materials, where normal processes are more important. The calculations reveal that the SnS monolayer has enhanced electrical performance as compared to the bulk phase. As a consequence, high figures of merit Z T ∼ 5 and Z T ∼ 1.36 are predicted at 600 and 300 K, respectively, for the monolayer, ∼ 33 times higher than the Z T of its bulk analog. Therefore, this structure is an interesting candidate for room-temperature thermoelectric applications. A comparison between the fully ab initio results and simpler models based on relaxation times for electrons and phonons highlights the efficiency of computationally inexpensive models. However, ab initio calculations are found to be very important for the prediction of thermal transport properties.