<p>Al-added low-density medium Mn steel is used in structural applications that require welding and/or joining. The present work deals with laser welding of low-density medium Mn steel (Fe–7.92Mn–2.7Al–0.88Si–0.21C) that has been developed in house via the melting–casting route. The cast alloy, after undergoing hot forging, hot rolling, and annealing, has been laser welded in a butt joint configuration to investigate its weldability. The results show that the Al-added medium Mn steel has been successfully laser welded in a butt joint configuration without any major weld defects in the weld region such as microcracks, pores, etc. The fusion zone (FZ) comprises dendrites of delta ferrite and martensite/austenite (M/A) constituents that are formed due to rapid cooling after laser welding. The presence of very fine retained austenite at the interface of lath martensite has been confirmed by transmission electron microscopy (TEM) and atom probe tomography (APT), attributed to carbon segregation. Additionally, the microstructural analysis reveals some of fine solidification pores (~ 1&#xa0;µm diameter) inside the M/A structure in the fusion zone, possibly due to entrapment of environmental gases during welding. The welded joint exhibits 100% strength efficiency (ratio of welded joint strength to base metal strength), but the efficiency, in terms of total elongation is reduced to ~ 62% compared to the base metal total, primarily due to the formation of hard zone in the weld region.</p> Graphical Abstract <p></p>