Directed energy deposition (DED) process involves complex cyclic reheating and rapid cooling, which probably lead to differences in microstructure and corrosion resistance from the wrought alloys. In the present study, the pitting corrosion resistance of 17–4 PH martensitic stainless steel component fabricated by wire-arc DED technique under as-fabricated and post-processing heat treated (1050 °C for 1 h + H900 aging) conditions were investigated. The pitting corrosion resistance was significantly improved after post-processing heat treatment as reflected by a noble shift in pitting potential from 230 to 490 mV. This is mainly attributed to the formation of the reversed austenite (3%), precipitation of the nano-sized face-centered cubic (fcc) Cu particles as well as the refinement of martensitic matrix. However, a lower repassivation ability was observed as the precipitation of CrNbN, resulting in a N depletion region nearby. Simultaneously, a micro-galvanic couple was created between the CrNbN and nearby region, which promoted initiation of the pits surrounding the particles. This work illustrates that post-processing heat treatment is an effective way to improve the corrosion resistance of the wire-arc DEDed 17–4 PH stainless steel and the precipitation of CrNbN should be carefully controlled due to its detrimental effect on the repassivation ability.