Rehabilitation of existing structures through strengthening is a topic of growing interest in a time where sustainability and management of available resources are crucial. For this purpose, new application of existing and novel materials may hold a key role. In a present research project, a ductile CFRP strengthening system has shown promising potential as a strengthening solution. The research project has successfully demonstrated how the optimized system can be used for ductile strengthening of existing reinforced concrete (RC) structures. Strengthening of prestressed structures, however, is an application where there have traditionally been challenges with obtaining the desired capacity increase in conjunction with satisfying stiffness and ductility. In the study presented in this paper, rectangular prestressed concrete beams (500 × 350 × 5500 mm) were tested while strengthened with the ductile CFRP strengthening system using a flexible adhesive. As a reference, the system was also applied in a fully bonded configuration using epoxy resin. The results show that the applied system facilitates a satisfying ductile response for the strengthened beams, also in the linear elastic phase, where stiffness is paramount. The flexible adhesive ensures full activation of the CFRP anchors, while also providing some strain compatibility in the cross-section and additional utilization of the CFRP material, similar to epoxy-bonded configurations. Consequently, the results show that the considered ductile CFRP strengthening system may be a viable solution for rehabilitation of existing prestressed structures.