Rhenium disulfide (${\mathrm{ReS}}_2$), a member of group VII transition metal dichalcogenides (TMDs), has attracted increasing attention because of its unique distorted 1T structure and electronic and optical properties, which are much different from those of group VI TMDs (${\mathrm{MoS}}_2$, ${\mathrm{WS}}_2$, ${\mathrm{MoSe}}_2$, ${\mathrm{WSe}}_2$, etc.). It has been proved that bulk ${\mathrm{ReS}}_2$ behaves as a stack of electronically and vibrationally decoupled monolayers, which offers remarkable possibilities to prepare a monolayer ${\mathrm{ReS}}_2$ facilely and offers a novel platform to study photonic properties of TMDs. However, due to the large and layer-independent bandgap, the nonlinear optical properties of ${\mathrm{ReS}}_2$ from the visible to mid-infrared spectral range have not yet been investigated. Here, the band structure of ${\mathrm{ReS}}_2$ with the introduction of defects is simulated by the ab initio method, and the results indicate that the bandgap can be reduced from 1.38 to 0.54 eV with the introduction of defects in a suitable range. In the experiment, using a bulk ${\mathrm{ReS}}_2$ with suitable defects as the raw material, a few-layered broadband ${\mathrm{ReS}}_2$ saturable absorber (SA) is prepared by the liquid phase exfoliation method. Using the as-prepared ${\mathrm{ReS}}_2$ SA, passively $Q$-switched solid-state lasers at wavelengths of 0.64, 1.064, and 1.991 μm are in