Ultra-High-Performance Concrete (UHPC) and Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) have revolutionized the construction industry with their exceptional mechanical strength, durability, and sustainability. This comprehensive review explores the material composition, structural applications, mechanical behavior, durability performance, and sustainability potential of UHPC/UHPFRC in civil structures. The study provides a critical analysis of recent advancements in mix design, highlighting the role of nanomaterials, fiber reinforcement, and alternative binders in enhancing performance. The review discusses key structural applications, including bridges, high-rise buildings, seismic-resistant structures, and protective elements, where UHPC/UHPFRC offers significant advantages in load-bearing capacity, impact resistance, and long-term durability. The integration of digital fabrication techniques, such as 3D printing, smart sensing, and AI-driven optimization, is also examined for its potential to improve structural efficiency and sustainability. Furthermore, the study evaluates the environmental impact and life-cycle benefits of UHPC/UHPFRC, emphasizing the reduction in material consumption, extended service life, and resilience against harsh environmental conditions. While UHPC/UHPFRC presents promising opportunities, challenges related to high initial costs, standardization, and large-scale adoption remain critical research areas. The findings of this review provide a comprehensive knowledge base for researchers, engineers, and policymakers, facilitating the development of next-generation construction technologies. Future research should focus on cost-effective material innovations, enhanced sustainability strategies, and broader industrial applications to unlock the full potential of UHPC/UHPFRC in modern civil engineering.