Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has found application in demanding structural scenarios requiring exceptional performance, durability, and ductility. The utilization of this material for structural strengthening is increasingly gaining popularity. It allows for the construction of slender, yet ductile elements without significant alterations to the element’s dimensions. One of the primary drawbacks of this material is the lack of extensive design codes. Additionally, its high cost is another notable limitation. The present study focuses on the application of UHPFRC for strengthening purposes and aims to investigate its optimal characteristics. In this study, the results from testing large-scale beams strengthened with UHPFRC layers have been used to develop a numerical model capable of predicting the performance of strengthened reinforced concrete beams. This model explores critical material parameters, including layer depth, fiber content, the interface condition, and the use of steel bars in the layers. The results suggest that incorporating additional reinforcing bars into the UHPFRC layers yields superior performance when compared to increasing the depth of the elements or using higher fiber dosages. The interface conditions affect the performance of strengthened elements significantly.