Previous studies have confirmed the vulnerability of reinforced concrete (RC) knee joints under cyclic loading, however, there remains a lack of studies on their seismic retrofitting. This study proposes a retrofit strategy aimed at enhancing the seismic performance of knee joints by acknowledging their unique behavior. The strategy involves a novel arrangement of steel plates that optimizes the effectiveness of steel haunch and external prestressing methods. To evaluate this approach, six full-scale knee joint specimens—two controls and four retrofitted—were fabricated using nonseismic reinforcement details and subjected to reversed cyclic loading. Vital parameters, including load, displacement, and strain responses along the reinforcement bars and steel plates, were monitored throughout the tests. The specimens retrofitted with this newly proposed strategy demonstrated a significant improvement in seismic performance by effectively distributing the prestressing force to the core of the joint and promoting beam flexural failure. The lateral strength significantly increased, with maximum enhancements of 100 % and 200 % under closing and opening rotations, respectively. Additionally, the retrofitted specimens dissipated at least 100 % more cyclic energy compared to the control specimens. Furthermore, the proposed distribution of the prestressing force within the joint core was instrumental in restraining the expansion of diagonal cracks. Consequently, this study makes a substantial contribution to the body of knowledge on RC knee joints and promotes their practical implementation under different conditions.