Parts with complex geometry, elevated mechanical and corrosion resistance can be obtained by martensitic stainless steels (MSS) using additive manufacturing by laser directed energy deposition (AM L-DED) process. In this work, a proposed method was employed for choosing L-DED parameters based on design of experiments (DoE): Single beads, to define windows of powder feed rate, laser power, and travel speed; Single layers, to find the ideal hatch spacing for lateral bead overlapping; and Multilayer, to determine the ideal layer height for layer overlapping. Using the optimized parameters, AM L-DED samples were produced of AISI 410L MSS feedstock on AISI 410 MSS substrate. Microstructure, hardness, tensile strength, and impact toughness were evaluated in the as built and heat-treated conditions and compared to the AISI 410 substrate. Four heat-treatment routes were investigated: annealed (1050 °C for 90 min and water quenched), and annealed, water quenched and tempered at 300 °C, 450 °C, and 600 °C for 90 min, then air cooling. From results, as built samples showed the highest hardness, yield and ultimate tensile strength, but the lowest toughness. Ductility was progressively recovered with tempering temperature increase. Best compromise was seen in samples tempered at 600 °C that showed toughness improvement, keeping a tensile performance higher than AISI 410 substrate.