Lignin is a natural, renewable biopolymer synthesized by plants. It is a macromolecule consisting of aromatic structures with high density of functional groups making it an ideal precursor for the design of sustainable biomaterials for applications such as drug delivery. The rational design of these materials requires an in-depth understanding of the underlying lignin self-assembly in solution. Colloidal transformations from nanosized lignin assemblies to submicron-sized spherical particles upon solvent exchange were studied using small-angle X-ray scattering, dynamic light scattering, and electron microscopy. The surface fractal structure and stability of these particles was found to be strongly solvent and pH dependent, with aggregation to a gel-like material at low pH. The results may have important implications for the design of nanostructured lignin-based functional materials for consideration in various fields such as food science and biomedicine.