<p>Nickel–copper alloy UNS N04400, also commonly known as Monel 400, is an alloy with excellent seawater corrosion resistance combined with good mechanical properties and is used in applications in the marine and nuclear energy industries. As it is a niche alloy, components can be costly to manufacture or replace; therefore, the benefit of laser powder bed fusion (LPBF) for this alloy is great. This work aims to provide a comprehensive exploration into the process window for the most influential parameters: laser power, scan speed, and hatch spacing. A series of statistical experiments following design of experiment principles was employed to determine the response of the density and surface topography of the LPBF Monel 400. Density of up to 99.9% was achieved. It was found that while high energy density resulted in less porosity, it also typically resulted in unstable melt pools. Microstructure analysis was carried out to confirm the effects of the process parameters on the resulting porosity. As expected, insufficient energy led to lack of fusion porosity, while high energy caused increased keyhole porosity. The effect of rapid solidification from LPBF on the grain structure and segregation was also examined through electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), respectively. The microstructure demonstrated evidence of epitaxial grain growth and fine-scaled micro-segregation of alloying additions as commonly observed in LPBF products. </p>