In this study, we propose a novel compliant active-force support system (CAFS) to provide force sensing and control capabilities in supports of thin-walled parts for precision machining. The CAFS is designed with a dual-feedback parallel mechanism (DFPM) driven by a piezoelectric actuator. Through displacement amplification, the DFPM enables CAFS to provide an active force support for compliant machining. Based on the input and output feedbacks of the DFPM, the contact force between CAFS and workpiece can be derived by the built force-sensing model, and the deformation of workpiece can be measured. Meanwhile, with the obtained force as feedback, the support force can be controlled by adjusting the displacement of piezoelectric actuator in real time. Without needing additional force-sensing components, a fast dynamic response can hence be achieved by the proposed CAFS. The performance of the CAFS is predicted by an established analytical model, and validated by finite element analysis and experiment. The results show that the developed CAFS prototype with a size of 56 mm56 mm93 mm can provide a 220 N support force with a resolution of 0.35 N (0.16%). The first resonant frequency of the developed CAFS prototype can reach 4,844 Hz. Closed-loop experiments further demonstrate that the proposed CAFS is capable of regulating the support force in a fast and accurate manner.