Although the structural and electrical engineering of transition metal dichalcogenides using atomic doping or doping‐induced phase modulation can be used to attain high‐performance and wavelength‐tunable optoelectronic devices, accessible substitutional doping to overcome the large lattice mismatch between the host and guest atom‐related bonding states remains elusive. This study corroborates an innovative synthetic route for molybdenum disulfide (MoS2)‐derived two‐dimensional (2D) quaternary semiconductors substitutionally doped with Re and O using a solution‐based large‐area compatible approach combined with the thermal evaporation of dopants. The substitutional doping of Re into MoS2 crystals with a large lattice mismatch is effectively accomplished by adopting structurally unstable host films, resulting in the large‐scale synthesis of 2D quaternary multi‐layers with a Re doping concentration >10%. Comprehensive spectroscopic and microscopic evaluations are performed to determine the efficacy of the host films with structural instability for the synthesis of 2D RexMo(1‐x)O2yS2(1‐y) quaternary multi‐layers. The capability of the quaternary semiconductor for versatile nanophotonic devices is validated by ascertaining the simultaneous enhancement of the photoelectrical properties with wide‐range optical absorption and photoelectrochemical properties, as compared with those of their binary counterparts.