Dissimilar joints of steel and aluminum are in great demand in shipbuilding applications, such as connecting steel hulls to aluminum superstructures. For this welding application, an explosive-welded adapter is used, which manufacturing is complex and cost-intensive. Searching for alternative welding processes, laser beam welding has emerged due to its specific advantages. Compared to other fusion joining processes, laser beam welding enables a better control of the weld metal mixing ratio and thus the microstructure. To achieve a constant weld metal mixing ratio and thus homogeneous microstructure over the weld seam length, an in-process control of penetration depth based on the analysis of spectral process emissions for lap welding of steel S355 (t = 5 mm) and aluminum alloy AA6062 (t = 12 mm) with two intersecting laser beams is developed in these investigations. The main result of using the process control is that the microstructure and the joint strength remain almost constant, despite varying welding speeds.