Obesity alters lipid profile, blood glucose, liver enzymes, oxidative stress, and hormonal balance. Fennel has shown anti-obesity effects in preliminary studies, but its role in ameliorative metabolic complications of obesity needs further research. This study assessed the provisional influences of fennel extract against high-fat diet-provoked metabolic deviations in rats. Forty male albino rats were allocated into standard diet control, obese control, low dose fennel (100 mg/kg) and high dose fennel (300 mg/kg) groups. Obesity was triggered by 4 weeks of high-fat nourishment. Fennel extract was applied orally for 6 weeks. Parameters considered were body weight, lipid profile, blood glucose, liver enzymes, antioxidant status, thyroid hormones, leptin, and hepatic insulin receptor gene expression. Fennel significantly diminished body weight, total cholesterol, triglycerides, LDL-cholesterol, liver enzymes, glucose, and leptin while increasing HDL-cholesterol, antioxidant enzymes, and thyroid stimulating hormone compared to obese controls. Histological examination has shown alleviation of fat accumulation and intracellular changes in the liver. Insulin receptor gene expression was also significantly increased by fennel extract. This study demonstrated that fennel extract reverses obesity-induced metabolic syndrome, oxidative stress, endocrine disruption, and histopathological change in the liver of rats. The hypolipidemic, hypoglycemic, antioxidant, and hepatoprotective properties of fennel may be beneficial in managing obesity-associated metabolic complications.