Additive manufacturing (AM) is considered a substitute for traditional manufacturing routes, considering the capacity to construct near-net shape products with complex shapes and geometries, which are considered inconceivable by conventional methods. Nevertheless, AM parts exhibit poor surface morphology, needing the assistance of post-print machining operations for surface quality improvement. However, using the process parameters reserved for machining conventional materials can lead to unoptimized cuts, lowering the surface finish, accelerating the tool wear, and decreasing the machining efficiency. The present work evaluates the post-milling surface finish of forged and AM 18Ni300 maraging steel. The selected feed and cutting speed influenced the surface roughness of conventional and AM materials. Surface roughness decreased by 99–148% as cutting speed increased from 20 to 40 m/min while milling conventional alloy. Whereas in the case of AM material a 68–271% decrease in surface roughness was observed. However, an increasing trend was observed with the feed value for both materials. A 176–230% increase in the surface roughness was observed as feed increased from 0.06 to 0.18 mm/rev, while milling the conventional material. For the similar increase in feed, a 244–324% increase in surface roughness was recorded while milling AM material. Additionally, surface roughness was influenced by the kind of material that is being machined. The surface roughness was lower by 17.3–48.2% lower for the AM specimens than the conventional specimens. The difference in the surface generated is primarily due to the inherent differences in ductility, plastic deformation characteristics, and microstructure between the two materials.