Molecular self-assembly under kinetic control is expected to yield nanostructures that are inaccessible through the spontaneous thermodynamic process. Moreover, time-dependent evolution, which is reminiscent of biomolecular systems, may occur under such out-of-equilibrium conditions, allowing the synthesis of supramolecular assemblies with enhanced complexities. Here we report on the capacity of a metastable porphyrin supramolecular assembly to differentiate into nanofibre and nanosheet structures. Mechanistic studies of the relationship between the molecular design and pathway complexity in the self-assembly unveiled the energy landscape that governs the unique kinetic behaviour. Based on this understanding, we could control the differentiation phenomena and achieve both one- and two-dimensional living supramolecular polymerization using an identical monomer. Furthermore, we found that the obtained nanostructures are electronically distinct, which illustrates the pathway-dependent material properties.