Background: Recently, crop byproducts are considered a hot topic and can be converted into beneficial products. Cauliflower is well-known for its protective effects against oxidative stress-induced damage. The current study aimed to investigate the chemical profile and the ameliorative effects of cauliflower leaf extract (CL) on gentamicin-induced renal and hepatic injuries in rats. Methods: Cauliflower leaf was extracted with methanol to give the total methanol extract (TME) followed by the determination of total phenolic contents (TPC). Rats were divided into five groups; Group I was assigned as the control group, while the other groups were injected with gentamicin for ten days. Group II was given distilled water. Rats in groups III and IV were treated with oral CL (200 mg/kg and 400 mg/kg, respectively). Group V received L-cysteine (as a positive control). The functions of the kidneys and liver; oxidative stress and morphological and apoptotic changes of renal and hepatic tissues were assessed. Results: The TME was subjected to chromatographic techniques to yield ferulic acid, vanillic acid, p-coumaric acid and quercetin. TPC was 72.31 mg GAE/g of dried extract. CL treatment dose-dependently ameliorated gentamicin-induced impaired kidney and liver functions and improved the histopathological appearance of both organs. It also reduced gentamicin-induced oxidative stress. CL demonstrated downregulation of mRNA and protein expressions of IL-1β and NF-κB compared to nontreated rats. In silico interaction of the isolated compounds with amino acid residues of IL-1β and NF-κB might explain the current findings. Conclusion: Taken together, this study raises the waste-to-wealth potential of cauliflower to mitigate gentamicin-induced hepatorenal injury and convert the waste agromaterials into valuable products.