The feasibility of designing a subcritical Flexible Matrix Composite (FMC) helicopter driveshaft is examined in this research. A finite element model of the tailboom/driveline structure is derived to predict driveshaft properties, including natural frequencies, failure strength, critical buckling torque, critical yield torque, and maximum shaft temperature. Through analyzing the model, it is shown that the laminate parameters can significantly affect the system performance and weight, and the advantages of altering the laminate configuration are discussed. Shaft design parameters such as number of plies, ply sequences, and number of midspan bearings are tailored to provide minimum weight while satisfying system performance requirements. It is illustrated that the FMC structure can provide improved performance while reducing weight and number of components in the driveline system. Several sets of shaft parameters are presented that satisfy system requirements while reducing weight and number of components compared to current drivelines on the UH-60 Blackhawk and CH-47 Chinook. For the best case study on the Blackhawk, a single FMC shaft can reduce driveline weight by approximately 29% (9 kg) while eliminating five driveline components. For the Chinook, the best case study shows that a single FMC shaft can reduce driveline weight by 26% (15.2 kg) while eliminating seven driveline components.