This narrative review systematically evaluates the therapeutic potential and mechanisms of action of Arctii Fructus lignans (from Arctium lappa L.) in managing diabetes mellitus (DM) and its complications. To ensure a comprehensive evidence synthesis, a systematic literature search was conducted using PubMed, Web of Science, CNKI, and Wanfang Data for publications between January 2000 and June 2024. Study selection was based on predefined inclusion and exclusion criteria focusing on lignan-specific antidiabetic effects and mechanistic insights. The accumulated evidence demonstrates that Arctii Fructus lignans exhibit multi-targeted pharmacological effects through several key mechanisms: (1) improving glucose homeostasis via α-glucosidase inhibition and AMPK/PI3K pathway activation; (2) protecting pancreatic β-cell function through anti-inflammatory and anti-apoptotic actions; and (3) mitigating diabetic complications by reducing oxidative stress, modulating TGF-β/VEGF signaling, and restoring autophagy balance. Notably, these lignans show particular efficacy in early-stage diabetes models, with reduced effectiveness in advanced stages featuring significant β-cell dysfunction, suggesting a critical therapeutic window for intervention. Future research should prioritize well-designed clinical trials using standardized extracts, investigations into structure–activity relationships, and exploration of synergistic effects within traditional formulations to advance the translational potential of these promising natural compounds.