We report the fibril formation of poly(-glucose carbonate) (PGC)-based amphiphilic diblock copolymers using solution assembly. Unlike conventional cylindrical micelles constructed from amphiphilic block copolymers (BCPs) with coil-like blocks, the assembled PGC fibrils exhibit thin, ribbon-like features due to significant stiffness and hydrophobicity of the PGC BCP backbone that result in a unique polymer chain packing. A tetrahydrofuran/H2O solvent mixture was used to create a solvent quality gradient during which a hierarchical assembly pathway was observed with fibril precursor nanoparticles that linked together into fibrils. These initial precursors were soft, patchy nanoparticles caused by the phase-segregated hydrophilic block of the PGC diblock copolymer. With aging, the patchy nanoparticles underwent unidirectional attachment through hydrophobic association to transform into uniform fibril structures. Transmission electron microscopy, interpretation of the small-angle neutron scattering measurements fit with analytical models, and genetic algorithm-based reverse engineering of structure confirmed the presence of initial particle precursors, intermediate stages during growth, and the fully matured fibrils. The results suggest that unconventional backbone chemistry-based molecules reveal unique effects of chain stiffness and hydrophobicity on block copolymer solution assembly when using glucose-based polycarbonates.