Disclosed herein are a method of forming a transition metal dichalcogenide thin film and a method of manufacturing a device including the same. The method of forming a transition metal dichalcogenide thin film includes: providing a substrate in a reaction chamber; depositing a transition metal dichalcogenide thin film on the substrate using a sputtering process that uses a transition metal precursor and a chalcogen precursor and is performed at a first temperature; and injecting the chalcogen precursor in a gas state and heat-treating the transition metal dichalcogenide thin film at a second temperature that is higher than the first temperature. The substrate may include a sapphire substrate, a silicon oxide (SiO2) substrate, a nanocrystalline graphene substrate, or a molybdenum disulfide (MoS2) substrate.