Protective immunity against pathogens depends on the efficient generation of functionally diverse effector and memory T lymphocytes. However, whether plasticity during effector-to-memory CD8⁺ T cell differentiation affects memory lineage specification and functional versatility remains unclear. Using genetic fate mapping analysis of highly cytotoxic KLRG1⁺ effector CD8⁺ T cells, we demonstrated that KLRG1⁺ cells receiving intermediate amounts of activating and inflammatory signals downregulated KLRG1 during the contraction phase in a Bach2-dependent manner and differentiated into all memory T cell linages, including CX₃CR1^int peripheral memory cells and tissue-resident memory cells. "ExKLRG1" memory cells retained high cytotoxic and proliferative capacity distinct from other populations, which contributed to effective anti-influenza and anti-tumor immunity. Our work demonstrates that developmental plasticity of KLRG1⁺ effector CD8⁺ T cells is important in promoting functionally versatile memory cells and long-term protective immunity.