Obesity is a global health challenge closely linked to gut microbiota dysbiosis. This study investigated the anti-obesity effects of Bifidobacterium breve B2798 in a high-fat diet (HFD)-induced mouse model. Male C57BL/6 mice were fed a 60% HFD with or without daily oral administration of B. breve B2798 12 weeks. Probiotic intervention significantly reduced body weight gain, visceral adiposity, and hepatic steatosis compared to the HFD group. Serum lipid profiling revealed increased HDL-C levels in the probiotic-treated group, indicating improved metabolic health. Fecal metagenomic analysis showed that B. breve B2798 reshaped the gut microbiota, enriching beneficial taxa such as Ligilactobacillus while reducing pro-inflammatory Faecalibaculum rodentium. Untargeted metabolomics of fecal and serum samples revealed significant modulation of metabolic pathways, including bile acid metabolism, amino acid biosynthesis, and short-chain fatty acid production. Key metabolites such as chenodeoxycholic acid, limonin, azelaic acid, and syringic acid were elevated in the B. breve B2798-treated group and are linked to anti-obesity and anti-inflammatory effects. Integrated correlation analysis demonstrated strong associations between microbial shifts, metabolic changes, and improved phenotypes. These findings, obtained in a murine model, suggest that B. breve B2798 alleviates obesity through a gut microbiota-host metabolic axis, offering a promising adjunctive probiotic strategy for metabolic disease prevention.