BiOBr_xI_1−x composite photocatalysts have been successfully deposited on carbon nanofiber (CNF) substrates via two steps. The first step involves an electrospinning technique and the second step includes a one-pot solvothermal method. The characterization results show that a large number of BiOBr_xI_1−x nanoflowers are deposited on carbon nanofibers, and the diameters of the BiOBr_xI_1−x/CNF composites are 0.7–1.2 μm. Due to the high electrical conductivity, the CNF could easily capture and transfer electrons, resulting in the effective separation of photoinduced charges. As a result, the BiOBr_xI_1−x/CNF photocatalysts show a dramatically improved photocatalytic degradation and nitrogen fixation, due to the enhanced light harvesting and effective photoinduced charge separation. Additionally, the increased water oxidation capacity of the BiOBr_xI_1−x/CNF is also important to enhance the photocatalytic activity. The BiOBr_xI_1−x/CNF samples also show excellent photochemical stability. This study stresses the significance of the synthesized CNF/semiconductor photocatalysts with high potential for practical applications.