Fusarium wilt, caused byFusarium oxysporumf. sp.niveum(Fon), poses a serious threat to watermelon productivity. We previously characterized six antagonistic bacterial strains, including DHA6, capable of suppressing watermelon Fusarium wilt under greenhouse conditions. This study investigates the role of extracellular cyclic lipopeptides (CLPs) produced by strain DHA6 in Fusarium wilt suppression. Taxonomic analysis based on the16S rRNAgene sequence categorized strain DHA6 asBacillus amyloliquefaciens. MALDI-TOF mass spectrometry identified five families of CLPs, i.e., iturin, surfactin, bacillomycin, syringfactin, and pumilacidin, in the culture filtrate ofB. amyloliquefaciensDHA6. These CLPs exhibited significant antifungal activity againstFonby inducing oxidative stress and disrupting structural integrity, inhibiting mycelial growth and spore germination. Furthermore, pretreatment with CLPs promoted plant growth and suppressed watermelon Fusarium wilt by activating antioxidant enzymes (e.g., catalase, superoxide dismutase, and peroxidase) and triggering genes involved in salicylic acid and jasmonic acid/ethylene signaling in watermelon plants. These results highlight the critical roles of CLPs as determinants forB. amyloliquefaciensDHA6 in suppressing Fusarium wilt through direct antifungal activity and modulation of plant defense responses. This study provides a foundation for developingB. amyloliquefaciensDHA6-based biopesticides, serving as both antimicrobial agents and resistance inducers, to effectively control Fusarium wilt in watermelon and other crops.