This paper presents the design, development, and testing of a novel three-degree-of-freedom compliant parallel-kinematic active constant-force stage. The active constant-force property enables a large travel and constant driving property, which is enabled by introducing symmetrical bistable flexure hinges. The folded flexure mechanism is adopted to guide the driving input and to balance the stiffness of the stage to zero. Besides, leaf flexure hinges are employed to decouple the cross-axis motion of the three-degree-of-freedom parallel stage. Analytical modeling is conducted to evaluate the stage performances of constant-force property and motion decoupling, which is verified by performing finite-element analysis simulation study. Design optimization of the stage parameters is implemented for minimizing the fluctuation of the constant-force value via multi-objective genetic algorithm. Moreover, a prototype is fabricated and experimental study is carried out to validate the analytical modeling results and performances of the proposed stage design.