The European Commission has set a target to reduce greenhouse gas (GHG) emissions from road transport by 60\% compared to 1990 levels by 2050, as outlined in the Transport White Paper. In 2012, passenger cars accounted for about 60\% of GHG emissions from the road transport sector, a figure expected to decline to 45\% by 2030. Meanwhile, heavy-duty vehicles (HDVs), including trucks, buses, and coaches, contribute around 26\% of total CO$_2$ emissions in the European Union, with trucks alone responsible for over 85\% of this share. To achieve the 2050 goal, the European Commission has identified key strategies, including improving vehicle efficiency, developing sustainable propulsion systems, and using advanced lightweight material solutions. A promising approach to reduce fuel consumption and increase payload capacity in HDVs is to reduce vehicle weight. One method is the integration of ultra-high strength steels (UHSS) into chassis structures, enabling thinner, lighter components. However, the limited ductility of UHSS in cold-forming requires exploring alternative forming techniques. Warm forming of thick-walled UHSS sheets presents a viable solution. This thesis focused on the mechanical characterisation of WARMLIGHT-980, a novel 7~mm thick UHSS grade (UTS 980~MPa), developed for warm forming in the 430–580\textdegree C range. The goal of the forming process is to produce lightweight components with high stiffness and fatigue resistance, specifically for HDVs. The elastoplastic and ductile failure properties of this UHSS grade were investigated at elevated temperatures to support numerical simulations of warm-forming processes. Failure strains under various stress triaxialities and specimen geometries were determined by digital image correlation. Due to the thickness of the material, conventional full-scale specimens were impractical; thus, scaled-down 1.2~mm specimens were tested and validated against full-thickness tensile tests. Inductive heating was used to reach target-forming temperatures, with thermal photography confirming uniform distribution. A modified Mohr-Coulomb ductile failure model, calibrated at 3D stress states, was used to predict crack formation during forming. The thermo-mechanical simulation model was validated through three-point bending tests by comparing force-displacement responses. Thickness distribution from simulations was also compared with demonstrator components. Findings indicate UHSS can be effectively warm-formed into complex components at elevated temperatures. The calibrated material model accurately describes material behaviour, with simulation results closely matching experimental force measurements. This research supports the development of lightweight, high-performance HDV structures through improved forming processes and material modelling.