Fast scanning calorimetry (FSC) was employed to analyze the crystallization kinetics of poly(butylene succinate) (PBS) graphene nanocomposites. The emphasis of the present study is the heterogeneous nucleation of the PBS crystals in the presence of graphene nanosheets. Graphene oxide nanosheets were first synthesized and then reduced and homogeneously dispersed into a PBS matrix. The internal structure of neat PBS and of the nanocomposite was investigated by transmission electron microscopy and wide angle X-ray diffraction analysis. The crystallization from the melt and from the glass studied at high cooling and heating rates via FSC appeared to be significantly promoted in the presence of graphene. The presence of secondary crystallization on heating and the higher crystal perfection observed were attributed to the formation of a graphene network inside the PBS matrix. The activation energies of melt and glass crystallization were combined in order to obtain one set of Hoffman–Lauritzen parameters for each system. Finally, the growth rate of PBS crystals appeared to be highly enhanced in the presence of graphene nanosheets.