Herein, temperature‐dependent long‐term behavior of polypropylene and its transversely loaded unidirectional glass fiber reinforced composite is investigated and a lifetime prediction method is proposed, which is based on the observed long‐term failure mechanisms. Furthermore, the effect of cooling rate during processing on the time‐dependent behavior is addressed. The composite is revealed to exhibit multiple molecular deformation mechanisms, similar to neat polypropylene, which is modeled using the Ree–Eyring approach. Failure kinetics under constant‐strain‐rate and creep tests are found to be identical and switching from creep to cyclic loading decelerates the failure, which are signs of plasticity‐controlled failure. Hence, lifetime is predicted well by using a lifetime prediction methodology for the plasticity‐controlled failure which combines the Ree–Eyring approach and the concept of critical strain. A change in the cooling rate alters the deformation and failure kinetics: lower cooling rates promote embrittlement.