This study used a targeted metabolomics approach to examine changes in metabolites within green tea infusions fermented by G. lucidum (TFG) and evaluate the in vitro antioxidant and lipid-lowering properties of TFG. Fermentation decreased tea polyphenols, flavonoids, caffeine, soluble sugars, theaflavins, and catechins, while increasing free amino acids and theabrownins. The microbial bioconversion process led to the generation of decorated flavonoids, phenolic acids, terpenoids, alkaloids, nucleotides, and amino acids. This process shifted the tea’s taste from bitter and astringent to mellow, primarily due to the transformation of flavonoid glycosides, caffeine, catechins, 5′-guanosine monophosphate, 5′-uridine monophosphate, and theabrownins. Volatile metabolites added woody, floral, sweet, and fruity aromas. Reduced gallic acid and catechins lowered antioxidant activity, whereas increased theabrownins enhanced lipid-lowering activity and imparted a reddish-brown color. These findings indicate that fermentation significantly affects the flavor, aroma, and lipid-lowering ability of green tea infusion.