Abstract: The complex producing procedures and high energy-consuming limit the large-scale production and application of advanced high-strength steels (AHSSs). In this study, the direct strip casting (DSC) technology with unique sub-rapid solidification characteristics and cost advantages was applied to the production of low-alloy Si–Mn steel with the help of quenching & partitioning (Q&P) concept to address these issues. Compared this method with the conventional compact strip production (CSP) process, the initial microstructure formed under different solidification conditions and the influence of heat treatment processes on the final mechanical properties were investigated. The results show that the initial structure of the DSC sample is a dual-phase structure composed of fine lath martensite and bainite, while the initial structure of the CSP sample consists of pearlite and ferrite. The volume fraction and carbon content of retained austenite (RA) in DSC samples are usually higher than those in CSP samples after the same Q&P treatment. DSC samples typically demonstrate better comprehensive mechanical properties than the CSP sample. The DSC sample partitioned at 300°C for 300 s (DSC-Pt300) achieves the best comprehensive mechanical properties, with yield strength (YS) of 1282 MPa, ultimate tensile strength (UTS) of 1501 MPa, total elongation (TE) of 21.5%, and product of strength and elongation (PSE) as high as 32.3 GPa·%. These results indicate that the excellent mechanical properties in low-alloy Si–Mn steel can be obtained through a simple process (DSC−Q&P), which also demonstrates the superiority of DSC technology in manufacturing AHSSs.