AbstractMany technologically relevant materials for advanced energy storage and catalysis feature reduced transition‐metal (TM) oxides that are often nontrivial to prepare because of the need to control the reducing nature of the atmosphere in which they are synthesized. Herein, we show that an ab initio predictive synthesis strategy can be used to produce multi‐gram‐scale products of various MgV_xO_y‐type phases (δ‐MgV₂O₅, spinel MgV₂O₄, and MgVO₃) containing V³⁺ or V⁴⁺ relevant for Mg‐ion battery cathodes. Characterization of these phases using ²⁵Mg solid‐state NMR spectroscopy illustrates the potential of ²⁵Mg NMR for studying reversible magnesiation and local charge distributions. Rotor‐assisted population transfer (RAPT) is used as a much‐needed signal‐to‐noise enhancement technique. The ab initio guided synthesis method is seen as a step forward towards a predictive synthesis strategy for targeting specific complex TM oxides with variable oxidation states of technological importance.