Abstract: To enhance nutrient utilization efficiency in tobacco fields and to reduce the need for chemical fertilizers, a laboratory cultivation experiment, a pot experiment, and a field trial were conducted to explore the ability of a newly isolated brown-rot fungus, Fomitopsis palustris CQ19, in mobilizing soil nutrients, producing indole acetic acid (IAA) and siderophore, as well as improving soil fertility and promoting the growth of flue-cured tobacco. The results showed that CQ19 effectively mobilized insoluble nitrogen, phosphorus, and potassium sources such as peptone, lecithin, tricalcium phosphate, and potassium feldspar, and secreted IAA and siderophore. Under soil culture conditions, the fungal hyphae penetrated the soil, reduced soil pH, and significantly increased the contents of NH₄⁺-N, water-soluble phosphorus, and water-soluble potassium. In the pot experiment, CQ19 enhanced nitrate reductase activity and tobacco plant root vigor, and significantly increased plant biomass and nutrient uptake. The field trial revealed that CQ19 significantly increased the contents of NH₄⁺-N and water-soluble phosphorus, as well as soil protease and phosphatase activities. Correlation analysis showed that alkaline hydrolyzable nitrogen, NH₄⁺-N, and water-soluble phosphorus were critical factors affecting tobacco yield and quality. Furthermore, treatment with a 15% reduction in fertilizer combined with a fungal inoculant achieved tobacco yield and quality comparable to that achieved with conventional fertilization treatment. In conclusion, F. palustris CQ19 can effectively mobilize soil insoluble nitrogen, phosphorus, and potassium nutrients, and secrete IAA and siderophore, which are beneficial for reducing the application of chemical fertilizers and promoting tobacco growth.