There is a global pressing need for shear strengthening of existing concrete infrastructure. Fibre reinforced polymer (FRP) composites can be effectively used to enhance the shear strength of existing infrastructure but the factors influencing the FRP shear contribution are still not well understood. Extensive studies examining the parameters influencing the behaviour of FRP shear-strengthened concrete members are needed if the strengthened behaviour is to be fully understood. The Finite Element Method provides a cost-effective tool for numerically carrying out such studies. This research provides insight into the shear behaviour of prestressed concrete (PC) and reinforced concrete (RC) girders shear-strengthened with externally bonded FRP laminates or deep embedment FRP bars, respectively. Two finite element models, incorporating a total strain rotating crack model for the concrete, were developed. The developed models were validated using published results. Extensive parametric studies were then carried out to identify the effect of various parameters on the shear behaviour of FRP-strengthened RC and PC beams. The numerical results were utilised to develop a new design model for RC beams shear-strengthened with deep embedment FRP bars. Unlike current design models, the proposed model accounts for the effect of the main influencing parameters, and hence it showed considerable accuracy.