The advanced high strength steels (AHSS), in particular, the multiphase steels, with high strength and good ductility have been developed and widely used for industrial applications. Investigations on the mechanical properties of AHSS, especially the damage and fracture behaviour, have attracted significant attention for further improvement of the material performance and the damage tolerant material design. The aim of this study is to experimentally characterize and numerically model damage of a dual-phase steel, DP1000, during plastic deformation under various loading conditions, including stress states, temperatures and strain rates. The study is performed at two different length scales, the macroscopic and microscopic scales. At the macroscopic level, an extensive experimental program is designed involving dog-bone specimens, notched tension specimens, central-hole specimens, and punch specimens to cover a wide range of stress states. These tests are performed at different loading conditions to obtain the plasticity and ductile damage/fracture description of material response at various strain rates and temperatures. Scanning electron microscopy (SEM) micrographs on the specimens’ thickness cross-sections and the fractographs on fracture surfaces are observed to identify and quantify the damage mechanisms of the DP1000 steel. Furthermore, the electron backscatter diffraction (EBSD) assisted in-situ bending tests under different temperatures are designed to reveal the damage mechanisms of the DP1000 steel in the microscale. In addition, a numerical approach combining the fine resolution representative volume elements (RVE) method and the crystal plasticity finite element (CPFE) method is developed to upscaling the plastic deformation and damage behaviour of the DP1000 steel under various temperatures, strain rates, and stress states from microscale to macroscale.