Selective laser melting (SLM) in a vacuum environment is a relatively new process. Although the material is expected to undergo a gradual heat change, which will influence the microstructure and creep properties of IN718, little research has been conducted to date. Here, we compared specimens built in vacuum (V-SLM) to those built in an Ar atmosphere (Ar-SLM). We investigated the microstructure and creep properties of V-SLM, and compared the V-SLM specimen to a conventional Ar-SLM specimen. The V-SLM specimen had a larger-grained texture, and the quantity of the δ phase was much lower. In addition, the V-SLM specimen had lower amounts of aluminum and titanium oxides, which improved the stability of the γ″ phase. Thus, the V-SLM specimen showed better creep life than the Ar-SLM, due to prevention of brittle fractures along the interdendritic regions.