Abstract: The synergistic enhancement of strength and toughness in ultra-high-strength automotive steels is a key approach to achieving both vehicle lightweighting and safety. This review systematically summarizes the microstructural design strategies and mechanical-property characteristics of four representative types of third-generation ultra-high-strength automotive steels, namely QP steels, medium-Mn steels, 22MnB5 hot-stamped steels, and Mn-Cr low-alloy steels, with particular emphasis on the similarities and differences in their strengthening and toughening mechanisms. The results show that QP steels stabilize retained austenite through martensitic transformation and carbon partitioning, thereby achieving a favorable combination of high strength and ductility, although their product of strength and elongation remains relatively limited. Medium-Mn steels obtain a relatively high fraction of retained austenite through austenite-reverted transformation and Mn/C partitioning, which markedly enhances tensile ductility, whereas their yield strength remains comparatively low. After hot stamping, 22MnB5 steels develop a fully martensitic microstructure and exhibit ultra-high strength, but their ductility reserve is clearly insufficient. Further optimization of these three steel systems is constrained, respectively, by insufficient retained-austenite stability, relatively high alloying costs, and the intrinsically low ductility of fully martensitic microstructures. In contrast, Mn-Cr steels adopt a low-alloy design strategy and achieve a favorable combination of ultra-high strength and good ductility, even with little or no retained austenite, through the synergistic effects of multiphase microstructural control, grain-refinement strengthening, dispersed second-phase precipitation, and interactions between precipitates and dislocations. This strategy provides a scientific basis for the alloy design of novel ultra-high-strength automotive steels and for the development of innovative strengthening and toughening approaches.