© 2015 American Physical Society. © 2015 American Physical Society. Once a light axionlike scalar field couples to the electroweak gauge bosons, its classical motion during reheating induces an effective chemical potential for the fermion number. In the presence of rapid lepton number (L)-violating processes in the plasma, such a chemical potential provides a favorable opportunity for baryogenesis via leptogenesis. We are able to demonstrate that L violation due to the exchange of heavy Majorana neutrinos is sufficient for a successful realization of this idea. Our mechanism represents a novel and minimal alternative to thermal leptogenesis, which turns out to be insensitive to the masses and CP-violating phases in the heavy neutrino sector. It is consistent with heavy neutrino masses close to the scale of grand unification and, quite complementary to thermal leptogenesis, requires the reheating temperature to be at least of order 1012GeV.