This study presents an application of thermomechanical treatment technique (cold rolling followed by aging treatment) to significantly enhance the mechanical properties of a novel lightweight austenitic steel (Fe-30.5Mn–8Al-1.0C), mainly focusing on the impacts of cold-rolling reduction and subsequent aging temperature on its microstructure, texture, and tensile properties. It has been found that the dislocation density increased with an increase in cold rolling reduction from 25 % to 45 % and reached a saturation at a reduction of 45 %, facilitating the activation of deformation twins and accelerating κ-carbide precipitation. The tensile strength of the steel exhibited significant improvement with increased cold-rolling reduction, owing to the combined effects of dislocation strengthening and the Hall–Petch mechanism. A tensile strength as high as 1.6 GPa was obtained in samples treated by 65 % cold rolling reduction. Aging treatment can generally enhance the ductility in most samples, owing to an improved work hardening capability induced by κ-carbide precipitation. Consequently, an optimum thermomechanical process, involving a 45 % cold rolling reduction followed by aging at 600 °C for 10 min, was established to achieve a better combination of tensile strength (1428 ± 35.8 MPa) and elongation (26.7 ± 1.3 %), showcasing its potential for applications demanding high strength and exceptional ductility.