Type 1 diabetes mellitus (DM) is characterized by hyperglycemia resulting from insulin deficiency. This is usually accompanied by a pro-oxidative environment, dyslipidemia and endothelial dysfunction, thus leading to several micro- and macro-vascular complications. This study investigated the potential benefits of a seasoning obtained from seedless red wine pomace (RWPS) in protecting against oxidative damage and preserving endothelial function in Type 1 DM, and the underlying mechanisms involved at the level of gene expression. The diet of streptozotocin (45 mg kg-1)-induced diabetic (DB) and control (CN) male Wistar rats (n = 5 rats per group) was supplemented with RWPS (300 mg per kg per day) or vehicle for 4 weeks. Characteristic indicators of DM such as increased food and water intakes and weight loss were significantly ameliorated in DB + RWPS rats, with a notable normalization in their fasting glycemic control and cholesterol profile. Plasma total antioxidant capacity (TAC) was substantially increased, and biomarkers of oxidative damage to lipids (F2-isoprostanes, 24.9%; malondialdehyde, 28.4%) and proteins (carbonyl groups, 5.91%) were significantly decreased. Nitric oxide availability tended to improve in plasma of DB + RWPS compared with DB rats. Insulin levels were increased (1.51-fold) and aortic tissue antioxidant enzymes such as mitochondrial superoxide dismutase (SOD2, 1.93-fold) were up-regulated. Other important genes for endothelial function, including endothelial β-nicotinamide adenine dinucleotide phosphate oxidase (NOX4), endothelial and inducible nitric oxide synthases (eNOS, iNOS), and angiotensin-converting enzyme-I (ACE), were non-significantly modulated, although certain potentially positive trends were observed. These results indicate that RWPS supplementation might be a useful nutritional approach to manage Type 1 DM and ameliorate its vascular complications.