Abstract: Objective The aim was to address the instability of welding quality and mechanical properties in laser-arc hybrid welding of medium-thick high-strength steel plates. Methods The effects of process parameters on the weld profile, microstructure, and mechanical properties of Q690D high-strength steel single-V groove joints were systematically investigated using the laser-arc hybrid welding process. Results Complete groove penetration (1.0 mm gap, 10 mm root face) was achieved during the root pass with a laser power of 15 kW, a welding current of 120–250 A, and a welding speed of 1.0 m/min. The welding current significantly influences joint plasticity and toughness. At a low current of 120 A, an excessively rapid cooling rate generates abundant martensite in the weld zone, which deteriorates impact toughness and causes bending performance to fail standards. Conversely, at 250 A, the weld zone microstructure transforms into acicular ferrite and bainite. The impact fracture is predominantly characterized by dimples, demonstrating excellent toughness and plasticity. Conclusion The welded joints produced with a laser power of 15 kW, a welding current of 250 A, and a welding speed of 1.0 m/min for the root pass, combined with a laser power of 2 kW, a welding current of 280 A, and a welding speed of 0.5 m/min for the filler and capping passes, exhibited strength, ductility, and toughness that satisfied the relevant standards.