This study developed a twinning-induced plasticity (TWIP) steel characterized by lightweight, high strength, and high toughness. Tensile tests were conducted at strain rates ranging from 10⁻⁴ to 6500 s⁻¹ using a universal testing machine and a Hopkinson bar to evaluate the material’s mechanical properties. A Johnson–Cook (J-C) constitutive model was developed based on the mechanical performance data for high-strain behavior. X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to analyze the microstructural evolution and fracture mechanisms of tensile specimens. The results show that the TWIP steel exhibits positive strain rate sensitivity (PSRS) under both quasi-static and dynamic strain rates. At high strain rates, the yield strength increased from 1133.0 MPa to 1430.6 MPa, and the tensile strength rose from 1494.3 MPa to 1640.34 MPa. The J-C model fits well at strain rates of 1000 s⁻¹ and 3000 s⁻¹, but fitting errors increase at higher strain rates due to the competition between thermal softening and strain hardening. XRD results reveal no significant phase transformation occurred during deformation, with twinning being the dominant mechanism. As the strain rate increased, deformation twins appeared in the material’s microstructure, inducing plastic deformation during tensile testing. The twin volume fraction increases progressively with the strain rate. At high strain rates, secondary twins emerge and intersect with primary twins, refining the grains through mutual interaction. The TWIP effect enhances the material’s mechanical performance by improving its strength and ductility while maintaining its lightweight nature.