The electrification of heavy-duty vehicles (HDVs) is essential for achieving zero-emission freight transport. Conventional 400–800 V powertrains face limitations in supporting megawatt-level fast charging and high continuous power due to excessive current, cable losses, and thermal stress. Recent advances in high voltage (i.e., 1.7 kV, 2 kV, 3.3 kV) silicon-carbide (SiC) power modules and charging standards such as the Megawatt Charging System (MCS, up to 1250 V) have enabled a new generation of 1.2 kV dc-link architectures for HDVs. This paper presents a comprehensive system-level evaluation of increasing the dc-link voltage from 800 V to 1.2 kV, covering the battery, inverter, and motor subsystems. The battery/charging and motor-level results are presented as analytical first-order assessments, whereas the inverter-level loss-modelling methodology is experimentally validated on a 250 kW, 1.2 kV dc-link SiC prototype. A virtual-prototyping framework is used to quantify inverter losses, thermal behavior, and volume trade-offs, and the switching frequency is optimized by jointly considering inverter and motor harmonic losses. Experimental results showthat the analytical models predict measured inverter losses within approximately 10% over the tested operating range. Under the representative charging assumptions adopted in this study, 1.2 kV dc-link voltage enables either an∼56% reduction in cable conduction losses or an∼33% reduction in cable mass, while the prototype achieves an efficiency of ∼99.12%, a specific power density of 49.4 kW/L, and a bounding-box-based volumetric power density of 20.83 kW/L. The results provide system-level assessment and experimentally supported inverter-level design guidance for 1.2 kV HDV powertrains.