The causal relationships between attention-deficit/hyperactive disorder (ADHD) and vascular risk factors remain insufficiently understood. This study aimed to comprehensively investigate the causal effects of ADHD on vascular risk factors and identify crucial mediators in these relationships. Utilizing instrumental variables from genome-wide association study (GWAS) datasets, we applied two-sample Mendelian randomization (MR) to explore the causal influences of ADHD on adiposity-related traits, blood pressure regulation, glucose metabolism, lipid profiles, lifestyle habits, chronic kidney disease, and systemic inflammation. Additionally, two-step MR was employed to evaluate the mediating effect of educational attainment (EA) in each newly established causal pair. Genetically determined ADHD was causally linked to increased body mass index (BMI, β = 0.054, p = 1.01E-08), waist-to-hip ratio (WHR, β = 0.041, p = 1.65E-07), waist circumference (WC, β = 0.048, p = 5.78E-15), body fat percentage (BF%, β = 0.024, p = 7.19E-05), risk of type-2 diabetes mellitus (T2DM, OR = 1.104, p = 6.07E-07), and number of cigarettes smoked per day (β = 0.094, p = 3.99E-06), earlier smoking initiation (β = 0.115, p = 2.71E-12), and higher levels of C-reactive protein (CRP, β = 0.054, p = 6.35E-14). Furthermore, EA was demonstrated to play a key mediating role in these causal relationships, with mediation proportions ranging from 41.67% to 11.30%. Our MR analyses supported the causal impacts of ADHD on several vascular risk factors, including BMI, WHR, WC, BF%, T2DM, early smoking initiation, cigarettes consumed per day, and CRP. Moreover, we recognized EA as a critical mediator underlying the established causal pathways. Overall, this study highlighted that individuals with ADHD were more likely to suffer from obesity, T2DM, poor lifestyle habits, and intense inflammation.