With growing global recognition of the nutritional value of blueberries, their cultivation has expanded significantly across various regions. However, gray mold disease, caused by Botrytis cinerea, remains a major challenge in postharvest storage and transportation. In this study, two strains—Trichoderma asperellum BBR–A and B. cinerea BC7–1—were isolated and identified from the blueberry rhizosphere and diseased leaves. Co-culture assays demonstrated that BBR–A exhibits potent antagonistic activity, rapidly suppressing the growth of the pathogen BC7–1 through mycoparasitic behaviors, including hyphal coiling, penetration, and degradation. Transcriptomic analysis revealed that upon interaction with BC7–1, BBR–A undergoes extensive reprogramming of carbon metabolism, with coordinated upregulation of genes encoding degradative enzymes, transporters, and stress-related proteins. Congo red staining and enzymatic activity assays further confirmed the enhanced secretion of extracellular enzymes and the increased cell wall-degrading capacity of BBR–A. On detached blueberry leaves, seedlings, and fruits, BBR–A treatment significantly delayed lesion expansion and reduced disease severity. Metabolomic profiling further demonstrated that BBR–A induces the marked accumulation of phenolic compounds, polyamines, and other antioxidant- and immunity-related metabolites in blueberry leaves, thereby maintaining host redox homeostasis and enhancing stress resilience. Collectively, these findings indicate that T. asperellum BBR–A effectively suppresses B. cinerea through multiple mechanisms, including antagonism, mycoparasitism, metabolic regulation, and the induction of plant defense responses, highlighting its strong potential for development as a biocontrol agent against blueberry gray mold.