Wire and arc additive manufacturing (WAAM) has increasingly attracted much attention from scientists worldwide due to its ability to produce medium to huge metallic parts with elevated material deposition rate, high material usage efficiency, less environmental effect, and low equipment costs. Nickel-based superalloys, especially Inconel 625 and 718, are the most popularly studied by the additive manufacturing (AM) research community because of their superior strength, good oxidation, and corrosion resistance. This paper provides a comprehensive review and the internal qualities (i.e., microstructure and mechanical characteristics) of Inconel alloys fabricated by WAAM technologies. Common defects of as-built parts, such as cracks, porosity, deformation, residual stress, and delamination phenomenon, which occur during the WAAM process, and feasible methods to improve the quality of the as-built parts were also discussed. This review paper contributes to a better understanding of the WAAM processes of Inconel alloys.