The transition of the ore-based steel industry will increase the global volumes of electric arc furnace (EAF) slag and introduce new components inherently associated with iron ore. For example, vanadium is expected to partition to the slag, and its implications on downstream slag valorization must be considered. Therefore, the present study addressed the effect of VOx concentration on characteristics relevant to valorization as a supplementary cementitious material (SCM). A synthetic water-granulated CaO‒SiO2‒MgO‒Al2O3‒FeOx‒VOx slag system was systematically varied in VOx. By incorporating VOx, the saturation of the divalent metal oxide solid solution (RO-phase) and crystallization of spinel were promoted. Furthermore, dicalcium silicate crystallized at higher temperatures, which suggested an overall greater tendency for crystallization with increasing VOx concentrations. The effect of adding VOx on the vitrified fraction of the slag was studied by Raman spectroscopy, indicating that vanadium was incorporated into network-forming structures, but still had a net depolymerizing effect. By standardized SCM reactivity testing, VOx concentration was found to improve the inherent reactivity of the slag, which was suggested to stem from the depolymerization and the fact that vanadium is not expected to introduce internal diffusion barriers upon slag particle dissolution. Consequently, incorporating VOx into future EAF slags should be further investigated for environmental aspects as the reactivity was not negatively affected.