To address the automotive industry′s demands for lightweight, safety, and energy efficiency, laser welding of high-strength and ultra-high-strength steels has gained widespread application. In this paper, laser lap welding of dissimilar ultra-high-strength steels QP1180 and 22MnB5 was conducted to explore their adaptability to the laser welding process. The influences of process parameters on the microstructure and mechanical properties of the laser-welded joints were studied using optical microscopy (OM), scanning electron microscopy (SEM), Vickers hardness tester, hydraulic tensile testing machine, and other equipment. The results showed that under the selected process parameters, full penetration was achieved in all welded joints. With the increase of heat input, the macroscopic morphology of the weld seam changed from "hyperbolic" to "inverted trapezoidal", and the width of weld seam and heat-affected zone increased with the increase of heat input. Hardness measurements revealed that hardness values increased with heat input, though no complete softening was observed. Tensile strength of the welded joints ranged from 595 to 610 MPa, while elongation at break varied between 17.1% and 18.1%. The tensile strength and elongation at break were both between QP1180 and 22MnB5, and the fracture position of the tensile specimen occurred at the base metal of the 22MnB5 side, showing a uniform distribution of dimpled morphology, which belonged to ductile fracture.