The current study focused on the antioxidant potential, α-amylase inhibitory activity, and hypoglycemic, hypolipidemic, and histoprotective (pancreas and kidney) effects of polyherbal emulsion on the alloxan-induced diabetic rats. Polyherbal formulations were prepared from extracts and oils of Nigella sativa (N. sativa), Citrullus colocynthis (C. colocynthis), and Silybum marianum (S. marianum). Out of nine stable formulations, one formulation named F6-SMONSECCE was found to be the best after its evaluation using antioxidant and in vitro α-amylase inhibition assay. The prepared herbal formulations showed significant (p < 0.05) antioxidant activity in terms of radical scavenging as 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferricreducing antioxidant power (FRAP) assays and also revealed the presence of a significant amount of total phenolic and flavonoid contents. "F6-SMONSECCE" (prepared with composition; Silybum marianum oil (SMO) + Nigella sativa extract (NSE) + Citrullus colocynthis extract CCE) was selected for an in vivo trial to ascertain its antidiabetic potential. The treatment dose was determined by using an acute toxicity trial on rats. Administration of alloxan (150 mg/kg b.w., i.p.) significantly (P < 0.05) augmented the blood glucose levels and lipid contents as total cholesterol (TC), triglycerides (TG), low-density lipoproteins (LDL-c), and very-low-density lipoproteins (VLDL-c). However, the levels of insulin and high-density lipoproteins (HDL-c) were found to be decreased, and the histopathological alterations were also found in the pancreas and kidney. The administration of the polyherbal formulation (F6-SMONSECCE) significantly attenuated the blood glucose levels (22.94%), TC (29.10%), TG (38.15%), LDL-c (27.58%), and VLDL-c (71.52%), whereas on the other side, the insulin (−149.15%) and HDL-c levels (−22.22%) were significantly increased. A significant histopathological normalization was observed in the pancreas and kidney tissues of the F6-SMONSECCE-treated rats. The current findings proposed that the prepared polyherbal formulation "F6-SMONSECCE" exhibited significant antioxidant, antilipidemic, and hypoglycemic potential and hence might be suggested as a remedy against diabetes or as a coadjuvant to synthetic medicines to maintain normal physiology.