The mechanical behaviour of as-built DED-produced 18Ni300 Maraging steel was studied by manufacturing a wall-like structure from which three different specimen types were obtained: specimens in which the loading direction was the same as the printing direction (vertical), specimens in which these two directions were perpendicular (horizontal), and bimetallic specimens in which the interface between the AISI 1045 substrate and the 18Ni300 steel was tested. The yield strength of the produced samples was $987.9\pm 34.2$, $925.9\pm 89.7$ and $486.7\pm 47.2$$\mathrm{M}$$\mathrm{Pa}$ for the vertical, horizontal and bimetallic specimens, respectively, while the elongation to failure was $9.4\pm 1.9$, $18.3\pm 2.3$ and $14.06\pm 0.6\%$ in the same order. The latter specimen failed within the substrate-comprised portion of the specimen. Additionally, the fracture surfaces were analysed through scanning electron microscopy, concluding that while both surfaces consist of dimples, the horizontal specimen presented microporosities with a reduced diameter. A microhardness analysis in the printed wall-like structure following the printing direction yielded an average hardness of $392\pm 21$ HV0.3, with fluctuations along the build direction mostly within one standard deviation.