This study investigates the effects of process parameters, including welding current, laser power, and welding speed, on the weld formation in laser-MAG hybrid backing welding of 12 mm thick Q345B test plates. A series of experiments were conducted to determine the optimal parameters for achieving full penetration backing welds. The results show that full penetration can be achieved with laser power set between 4.0 to 4.5 kW, welding current ranging from 200 A to 280 A, and a welding speed of 1.0 m/min. Under these conditions, the weld formation was satisfactory, with no detectable defects such as pores or cracks. It was observed that a higher welding current resulted in a fuller weld formation. The welding process demonstrated adaptability to mismatch conditions, accommodating gaps up to 1 mm and staggering of 1.5 mm. The tensile strength of the welded joints exceeded that of the base metal, and the bending performance was satisfactory, fulfilling the criteria for engineering applications.