The concept of multiscale fibrous reinforcements in cementitious matrices is characterized by a wide range of scales from distributed nanomaterials and chopped short fibers to continuous fibrous reinforcements. Based on fibrous reinforcements at multiple scales, this study elaborately optimizes mechanical behavior by tailoring the types and volume fraction of fibers and develops a cementitious composite, flexible ultra-high performance reinforced cementitious composite (FHPRC), with 160 MPa compressive strength, 36 MPa tensile strength, over 1% ultimate tensile strain, less than 0.1 mm crack width, and significant post-yield stiffness. FHPRC combines the superior strength and durability of ultra-high performance concrete (UHPC) with the high ductility and crack control capacity of engineered cementitious composite. We demonstrated the effectiveness of the material design strategy through experimental and numerical examinations. The effects of the types of short fibers (steel with a designed length of 13 mm and glass with a length of 50 mm), fiber-reinforced polymers (FRPs) (carbon and glass), and textile configuration on the flexural behavior were analyzed. To capture their flexural behavior, several numerical models have been developed to optimize FHPRCs. Furthermore, the layered shell finite element model (FEM) based on the smeared crack approach considerably simplifies the numerical effort required to simulate intense matrix cracking. However, no realistic constitutive model for any composite containing one or more reinforcing fibers for layered shell FEMs has been developed. Hence, an equivalent constitutive model for layered shells was established to analyze the flexural behavior of FHPRCs. The model proved that the combination of UHPC and carbon FRP textiles yielded a superior composite. The research results provide valuable insights into the evolving field of advanced construction materials and engineering.