The present investigation focused on formulating an effective biofungicide from the naturally occurring phylloplane fungus of Jasminum sambac (Jasmine) against the leaf blight pathogen, Alternaria alternata. The pathogen was isolated and identified using 18S rRNA analysis. The sequence was studied and submitted to NCBI (access number PV368447). A pathogenicity test was performed to confirm the causal organism’s pathogenicity. From the healthy leaves of Jasminum sambac, four different phyllosphere fungi, namely Aspergillus niger, Cladosporium sp, Fusarium sp, and Mucor sp, were isolated by the leaf impression method. The colony morphology of all the isolated fungi was studied and identified by lactophenol cotton blue (LPCB) staining. An antagonist activity test was performed using the four identified phylloplane fungi against the pathogen Alternaria alternata as a screening test before the formulation of the biofungicide. Aspergillus niger showed the highest activity among all the fungi. Based on the antagonistic activity results, Aspergillus niger was selected for the formulation of a biofungicide. Aspergillus niger spores were separated, and the spore suspension was mixed with carrier materials (coconut oil and glycerol) at different ratios. Coconut oil-based Aspergillus niger biofungicide was found to be better than glycerol-based Aspergillus niger biofungicide. The formulation was sprayed directly onto blight-affected Jasmine leaves for 10 days. It was observed that an Aspergillus niger spore-based coconut oil biofungicide significantly reduced leaf spots. Advantages of this formulation include cost-effectiveness, an alternative to chemical fertilizers, eco-friendliness, and improved efficacy.