Recently proposed processes for direct electroplating on nonconductive substrates offer numerous advantages. The industrial implementation of such processes is, however, hampered by lack of understanding. Presented here is a model for this class of processes based on three synergistic mechanisms : (i) stepwise propagation through the seed clusters that serve as sequentially activated microelectrodes, (ii) preferential accessibility to current of the sharp edge, and (iii) kinetics-based enhancement due to the fast propagation of an additive-free edge. The model has been computer simulated and verified by experiments of copper electroplating on nonconductive substrates.