In the manufacturing thick structural pipes recently a new process has been developed. This Paper describes this newly discovered process called Laser Hybrid welding. In laser hybrid welding two processes i.e. laser welding and Gas Metal Arc (GMA) welding are combined together to create synergistic effects. In laser GMA hybrid welding of plates with thicknesses of up to 20 mm, the problem of pore formation and of centre rib defects occurs frequently which have, up to now, not yet been subject to detailed scientific analysis. It was the objective of this research work to reduce these weld defects by weld parameter investigations (of a geometrical and also metallurgical nature) or to even avoid them completely. It was investigated to determine the extent to which shielding gas composition, (root) gap width and misalignment of the joining partners affect the techno-mechanical properties. For this purpose, the welds were subjected to non-destructive test methods (viz. visual inspections and X-ray examinations) and also to destructive test methods (viz. transverse sections hardness measurements, tensile tests and notch bending tests). The synergistic effects have been discussed in the light of the mechanical and metallurgical characterisations of the weldments. Optimum process parameters have been evolved which could tolerate up to 0.4mm root gap and 0.8mm of misalignment without causing any centreline cracking. Combinations of helium and argon gas shielding have been found to produce porous free welds. It has been concluded that it is possible to replace submerged arc welds by laser GMA hybrid welds in the manufacturing of longitudinally welded pipes.