With the aim of designing novel polymeric materials that exhibit superb mechanical performance and at the same time can sense stress, the hydrogen bonding ureidopyrimidinone (UPy) and covalent mechanochromic spiropyran (SP) are incorporated into one polymer structure to program the mechanical and mechanochemical responses of the materials. Excellent correlation between the molecular and microscopic structures and the macroscopic properties has been successfully demonstrated. Tensile tests reveal a combination of excellent mechanical properties, that is, high strength, high elongation at break, and high toughness. The superior mechanical properties are shown to be the consequence of the successive fragmentation of the hard domains formed by stacks of UPy dimers and the dissociations of UPy diners. Stress sensing before catastrophic failure is also readily achieved in the form of color changing, which coincides with the strain hardening event. Studies show that the fragmentation and dissociation events occur before the mechanical activation of SP.