Aging is a strong risk factor for atherosclerosis and aging significantly impacts immune cell populations and function. Immune cells are a major contributor to development of atherosclerosis; however, most preclinical atherosclerosis studies are performed in young mice. The role of aging on CD8 + T cells during atherogenesis remains unclear. Here we determined that depletion of CD8 + T cells attenuated atherogenesis in aged, but not young, mice. Furthermore, adoptive transfer of splenic CD8 + T cells from aged mice which contain a high proportion of memory T cells significantly enhanced atherosclerosis in young Cd8 -/- recipient mice compared with transfer of CD8 + T cells from young donor mice. Finally, we characterized T cells in healthy and atherosclerotic young and aged mice by single-cell RNA-sequencing (scRNAseq) and T cell receptor sequencing (TCR-seq). We found that with aging effector memory, central memory, and granzyme K + effector memory CD8 + T cells accumulate within atherosclerotic plaques, and aging induces transcriptomic changes related to CD8 + T cell activation, migration, cytotoxicity, and exhaustion. Overall, our study identifies memory CD8 + T cells as potential therapeutic targets for reducing atherosclerosis in older adults.