Macrophages play a critical role in defending against Staphylococcus aureus (S. aureus), a major human pathogen. Recently, there has been growing interest in the metabolic regulation of macrophage function; however, the specific role of lipid synthesis in macrophage activation remains poorly understood. This study demonstrates that fatty acid synthase (FASN), an enzyme integral to de novo lipogenesis, is significantly upregulated in macrophages during S. aureus infection. Notably, S. aureus engages in a functional interaction with proteasomes, inhibiting their activity through the PI3K/AKT/mTOR signaling pathway. This interaction results in reduced degradation of FASN, leading to elevated levels of this crucial enzyme. The increased expression of FASN is vital for macrophage-mediated pathogen clearance, as it facilitates the formation of lipid droplets (LDs), which in turn enhance the antimicrobial response against S. aureus, partly through the accumulation of the antimicrobial peptide CAMP. In a murine pneumonia model, deficiency of FASN correlates with increased bacterial burden, exacerbated lung inflammation, and a significant reduction in survival rates. Collectively, these findings underscore the essential role of FASN-mediated LD formation in macrophage activation and highlight potential therapeutic targets within the FASN and lipid metabolism pathways for the treatment of S. aureus pneumonia.