Stainless steels are characterized by excellent mechanical properties and high corrosion resistance. For this reason, they are deployed in challenging operational environments. Their alloy compositions are precisely tuned to meet the specific properties required for their application. However, the number of stainless steels available for metal additive manufacturing (AM) is still limited and most of them are pre-alloyed raw materials originally developed for conventional manufacturing processes. As a result, the range of material properties achievable by AM is incomplete, limiting the applicability of AM technologies such as Laser Directed Energy Deposition of Metals (DED-LB/M). With an innovative approach known as in-situ alloying, the chemical composition of pre-alloyed powder can be adjusted by mixing it with an additional powder material. This allows the material properties to be modified and efficiently adapted to specific applications. The aim of this study is to gain novel insights into the microstructure formation of a duplex stainless steel (DSS) in-situ alloyed with elemental powders and processed using DED-LB/M. Pure chromium, molybdenum, nickel and manganese powders were added to the DSS powder to adjust the chemical composition and the resulting material properties. Chemical analysis of the generated specimens by means of optical emission spectroscopy (OES) demonstrated that the target composition can be adjusted precisely via in-situ alloying. Heterogeneous two-phased microstructures were observed for all materials investigated by using optical and scanning electron microscopy. The element distribution within the resulting microstructures was examined by wavelength-dispersive X-ray spectroscopy (WDX). Phase formation, grain size distribution and texture were analyzed by electron back scattered diffraction (EBSD). In accordance to the calculated Cr- and Ni-equivalents, in-situ alloying with ferrite stabilizers such as Cr and Mo promoted a more ferritic microstructure. In contrast, by adding austenite stabilizers such as Ni and Mn to the DSS, more austenitic microstructures were generated. It was also found that the additions of elemental powders significantly influenced the resulting average grain size and crystallographic texture of the material. Based on these findings, an adoption of functional properties (e.g. mechanical properties, wear and corrosion resistance) is expected as well.