In this study, we report the synthesis of single-crystalline h-BN on Ni(111) under ultrahigh vacuum (UHV) conditions using hexamethylborazine (HMB) as a nonclassical precursor. The novel use of HMB facilitates the diffusion of methyl groups into the bulk of Ni(111), playing a critical role in the achievement of high-quality crystalline h-BN layers. The synthesis is performed on a 2 mm-thick Ni(111) single crystal and on a 2-μm-thick Ni(111) thin film on sapphire to evaluate the feasibility of synthesizing h-BN on industrially relevant substrates. Advanced microscopic and spectroscopic techniques confirm the successful synthesis of h-BN. The growth of h-BN was investigated by scanning tunneling microscopy and low-energy electron microscopy. Low-energy electron diffraction confirms the single crystallinity of the grown 2-dimensional layer. X-ray photoelectron spectroscopy confirms the presence of boron and nitrogen bonds at the same binding energies reported in the literature for h-BN. In contrast, photoemission electron microscopy allows identification of the presence of h-BN throughout the Ni(111) surface. This work advances the understanding of h-BN growth mechanisms on metal substrates and provides a foundation for improving synthesis methods to meet the demands of next-generation materials and devices.