Terazosin (TZ), a well-known antagonist of the α1-adrenergic receptor (α1-AR), has demonstrated protective effects on vascular endothelial cells (ECs) and reduced vascular stiffness in clinical studies. Endothelial dysfunction and oxidative stress are central drivers of cardiometabolic diseases such as diabetes, where sustained ROS burden accelerates EC senescence and barrier failure. These findings suggest its potential role in combating vascular aging and atherosclerosis; however, the underlying mechanisms remain partially understood. In this study, we investigated whether TZ can prevent atherosclerosis in ApoE−/− mice fed a high-cholesterol diet and aimed to elucidate the mechanisms involved. Our results showed that TZ significantly reduced plaque size, EC senescence, vascular permeability, and reactive oxygen species (ROS) levels, effectively inhibiting atherosclerosis independently of α1-AR signaling. In cultured primary human umbilical vein ECs (HUVECs), TZ inhibited EC senescence via the Pgk1/Hsp90 pathway. It enhanced the interaction between Hsp90 and the antioxidant enzyme peroxiredoxin 1 (Prdx1), leading to lower ROS levels—a key driver of cellular senescence. These findings were confirmed in atherosclerotic ApoE−/− mice. Furthermore, senescent ECs exhibited increased levels of vascular endothelial growth factor A (VEGFA) and decreased levels of angiostatin, contributing to higher vascular permeability and exacerbating atherosclerosis. TZ effectively reversed these changes. Overall, our study demonstrates that TZ primarily alleviates EC senescence and atherosclerosis through the Pgk1/Hsp90/Prdx1 pathway, highlighting Pgk1 activation as a strategy that may also mitigate endothelial dysfunction and oxidative stress in broader cardiometabolic contexts (e.g., diabetes), suggesting that TZ is a promising senomorphic agent for treating vascular aging and atherosclerosis in clinical settings and that Pgk1-targeted interventions could have implications beyond atherosclerosis.