Nucleation, the pivotal first step of crystallization, governs essential characteristics of crystallization products, including size distribution, morphology, and polymorphism. While understanding this process is paramount for the design of chemical, pharmaceutical and industrial production processes, major knowledge gaps remain, especially with respect to crystallization of porous solids. Also for nanocrystalline ZIF-8, one of the most widely studied metal-organic frameworks, questions regarding the species involved in the nucleation pathway and their structural and chemical transformations remain unanswered. By combining harmonic light scattering, inherently sensitive to structural changes, with NMR spectroscopy, which reveals molecular exchanges between particles and solution, we were able to capture the crystallization mechanism of ZIF-8 in unprecedented detail. Initially, oligomerization forms small, prenucleation clusters with an excess of protonated ligands in a pre-equilibrium state. When these clusters aggregate to form amorphous precursor particles, protonated ligands are released, leading to an amorphous charge neutral structure that subsequently transforms into crystalline ZIF-8 through intraparticle reorganization. Later stages involve solution-mediated Ostwald ripening, where the growth mechanism changes to incorporation of monomers from solution. Our results demonstrate the intricate link between charge, stoichiometric and structural evolution in MOFs, and open up pathways for managing crystallization through chemical control of precursor phases.