In recent years, Ultra‑High‑Performance Concrete (UHPC) has gained considerable attention as a suitable material for producing precast components such as manhole covers, owing to its very high mechanical strength, excellent durability, and enhanced post‑cracking behavior. In this study, the effects of different types of fibers and nanosilica on the microstructure and mechanical performance of UHPC‑based concrete manhole covers are investigated. First, the performance of three types of fibers—steel, glass, and polypropylene—each at a volume fraction of 1%, was evaluated in UHPC to determine the most suitable fiber for concrete manhole cover applications. Compressive strength, load-bearing capacity, and freeze–thaw resistance tests were conducted on the specimens in accordance with the Iranian National Standard. The results showed that the incorporation of fibers improved the compressive strength and load‑bearing capacity of the covers, with steel fibers exhibiting the greatest enhancement, increasing the compressive strength by 19% to about 180 MPa and increasing load capacity from 6 tons to 12.5 tons. In the next stage, 1% nanosilica was added to the mixture containing steel fibers. The presence of nanosilica increased the compressive strength to about 200 MPa and the load‑bearing capacity to 14 tons. Specimens containing steel fibers and nanosilica exhibited a lower reduction in strength after freeze–thaw cycling. Microstructural analyses using Scanning Electron Microscopy (SEM) and X‑ray Diffraction (XRD) revealed that nanosilica, through nucleation effects, pozzolanic reactions, and filler action, reduced porosity, increased matrix density, and improved the interfacial transition zone (ITZ) between fibers and matrix. The findings indicate that the combined use of steel fibers and nanosilica in UHPC enhances mechanical properties and durability, providing a sustainable and economically viable solution for concrete manhole covers from a life-cycle perspective.