Lightweight dissimilar materials that exhibit increased performance and functionality are of great interest in the field of automobiles to reduce fuel consumption and improve fuel economy. The properties of different lightweight materials are jointly utilised to achieve the product performance. In this study, dissimilar materials such as complex phase steel and aluminium alloy are joined using a high power fiber coupled diode laser. Laser processing parameters (laser power and scanning speed) are optimized such that the thickness of the intermetallics is minimum, so as to obtain maximum mechanical strength. The intermetallics formed at the weld interface are mostly aluminium rich, which are brittle in nature and deteriorate the strength of the joint. The microstructural characterization results showed that the depth of penetration of the weld increased with increase in laser power or decrease in scanning speed. The maximum depth achieved was 1200 μm at a laser condition of power 3 kW and 8 mm/s scanning speed. However, due to increased depth of penetration the intermetallic thickness also increased to 17 μm. Maximum mechanical resistance of 254 N/mm was achieved at a laser power of 4 kW and scanning speed of 12 mm/s, when the intermetallics thickness was in the range of 11 μm.