Reliable joining of dissimilar structural materials requires tailored surface engineering to ensure stable interfacial performance. This study investigates the influence of mechanical (grinding, sandblasting), chemical (etching), and femtosecond laser surface treatments on the adhesive bonding behavior of DP600 high-strength steel and carbon fiber-reinforced polymer (CFRP). Treatments were applied individually and in combination, and their effects on surface topography, surface energy, and lap-shear strength were evaluated. For DP600 steel, femtosecond laser processing caused only moderate changes in conventional roughness parameters but increased shear strength by up to 200% compared to the untreated condition, indicating that surface activation dominates over purely geometrical effects. In CFRP, laser irradiation significantly increased the developed surface area and enhanced shear strength by up to 185%. Although mechanical and chemical treatments improved adhesion, laser processing consistently provided additional strengthening, particularly through combined topographical and physicochemical modification. The results establish a clear relationship between surface processing and mechanical performance. Femtosecond laser treatment emerges as an effective and controllable surface-engineering approach for improving adhesive bonding in both metallic and composite substrates, with direct relevance to laser-assisted industrial joining technologies.