High-performance marine steel is essential for the marine industry worldwide. L907A low-alloy marine steel was developed by China independently and is now widely used in ship construction. In this study, the plasticity and ductile fracture behavior of L907A steel under various stress states are systematically investigated by experiments, mechanical modeling, and numerical simulations. Through the use of different microscopic methods, the initial microstructure of the material is well characterized. The constituent phases and grain morphologies of L907A introduce a good combination of strength and ductility and exhibit isotropic in-plane features. Specimens with various geometries are designed and tested to characterize the mechanical response of the L907A steel under various stress states ranging from tension to shear. The isotropic von Mises yield function with mixed Swift-Voce hardening law is used to characterize large deformation, while fracture initiation under various stress states is described by the Hosford-Coulomb model. A new parameter identification method, which combines hybrid numerical-experimental approach with simulated annealing optimization algorithm, is proposed to obtain the globally optimal model parameters. It is demonstrated that the calibrated model can predict the plasticity and fracture behavior of L907A with great accuracy. Finally, the mechanical performance of L907A is compared with competing marine steels (e.g., DH36 steel and EH36 steel). Results indicate that the yield stress of L907A is close to DH36 and higher than EH36, but its average strain hardening rate is lower than DH36 and close to EH36; the ductility of L907A is close to DH36 but worse than EH36. The fracture locus of L907A exhibits minimal stress state dependence compared to both DH36 and EH36.