Global warming and sustainability concerns rapidly increased the demand for magnesium alloys as a lightweight material in numerous industries. Most of the manufacturers are keen to replace the heavier materials with Mg alloys and looking for a solution to welding challenges to explore it for a broader range of applications. The laser welding technique is promising and most suitable for joining Mg alloys. In this work, Fibre Beam Laser Welding (FBLW) was used to weld AZ61 and AZ91 Mg alloys in butt configuration. The microstructure, tensile, microhardness and impact toughness properties of the prepared joint were evaluated. The columnar grains were witnessed in the fusion zone and variations in grain structure over the weld significantly influenced the mechanical properties of the joint. There was a reduction in tensile strength and elongation of the joint w.r.t. AZ61 Mg alloy was approx. 24% and 63%, respectively. The microhardness of the fusion zone was decreased due to a change in grain structure.