This research provides an experimental examination of the bending behavior of fire-damaged reinforced concrete beams under various conditions, followed by strengthening using Ultra-High-Performance Concrete UHPC. The research aims to understand the impact of fire on the residual mechanical attributes and bending responses of these beams across varying scenarios. It also gauges how much strength can be regained when reinforced with UHPC. The experiment involved fourteen simply supported reinforced concrete beams, each 1500 mm long, 100 mm wide, and 200 mm high. One of these beams served as a control, unaffected by any variables. The rest of the samples were split into five groups, distinguished by the amount of pre-loading while under fire, the fire’s temperature, and how many sides were exposed to the fire. The fire tests adhered to the ISO 834 and ASTM E119 standard time-temperature curves, considering the pre-load. Within each group, one specimen remained unreinforced, while the others were fortified using UHPC in two distinct methods: one in a U-shape and the other on the bottom side. All beams underwent a four-point bending test until they failed. For the beams, there was a decline in the ultimate load ranging from 18.57% to 46.01% when subjected to fire at temperatures of 500 ℃ and 800 ℃ respectively. Additionally, during fire exposure, the residual bearing capacity drastically declines as the load level rises. The U-shaped strengthening of fire-damaged beams amplified the load-bearing capacity by 194–354%, whereas bottom-sided strengthening increased it by 113–209%.