In this study, a fiber laser-MAG hybrid welding technology is adopted under the condition of a 10 kW laser output power. A single pass is performed with high efficiency through the welding of an 18 mm-thick EH36 marine high-strength steel plate, which realizes a good single-side welding and double-side forming technology without welding defects. The optimal process parameters of this test are 10 kW laser output power, 0 mm defocusing amount, 3 mm optical wire spacing, 400 A welding current, 31.1 V welding voltage, 14.2 m/min wire feeding speed, 20 mm wire extension length, 20 L/min protective gas flow, and 1.5 m/min welding speed. The microstructure and mechanical properties of the welded joints are studied using analytical testing equipments. Results show that the microstructure of the upper part of the weld (i.e., arc action zone) is characterized by pro-eutectoid ferrite growing in the columnar grain boundary in the form of side plates and strips and a small amount of granular ferrite in the columnar grain. The substructure in the columnar crystal mainly comprises lath martensite and acicular bainite, with a small amount of upper bainite. Meanwhile, the V-shaped banded structure is mainly composed of lath martensite and a small amount of acicular bainite. The weld microstructure of the lower part of the weld (laser action zone) is mainly composed of lath martensite. The structure of the welding heat-affected zone (HAZ) in the arc and laser action zones is mainly composed of lath martensite. The highest hardness of the welded joint in the arc and laser action zones appears in the HAZ. The laser action zone has the highest hardness, and then the V-shaped banded structure and the arc action zone of the weld. The average tensile strength of the welded joints at room temperature is 521 MPa, and all the tensile joints are fractured on the base metal. The positive bending test of the welded joints meets the standard requirements. The average impact energies of the weld metal, HAZ, and base metal at -20 ℃ are 57, 53, and 52 J, respectively. The mechanical properties meet the requirements of the classification society.