Elastomers are indispensable materials due to their flexible, stretchable, and elastic nature. However, the polymer network structure constituting an elastomer is generally inhomogeneous, limiting the performance of the material. Here, a highly stretchable elastomer with unprecedented strain‐stiffening capability is developed based on a highly homogeneous network structure enabled by a module assembly strategy. The elastomer is synthesized by efficient end‐linking of a star‐shaped aliphatic polyester precursor with a narrow molecular‐weight distribution. The resulting product shows high strength (≈26 MPa) and remarkable stretchability (stretch ratio at break ≈1900%), as well as good fatigue resistance and notch insensitivity. Moreover, it shows extraordinary strain‐stiffening capability (>2000‐fold increase in the apparent stiffness) that exceeds the performance of any existing soft material. These unique properties are due to strain‐induced ordering of the polymer chains in a uniformly stretched network, as revealed by in situ X‐ray scattering analyses. The utility of this great strain‐stiffening capability is demonstrated by realizing a simple variable stiffness actuator for soft robotics.