Cytotoxic T lymphocytes (CTLs) are pivotal in combating cancer, yet their efficacy is often hindered by the immunosuppressive tumor microenvironment, resulting in exhaustion. This study investigates the role of interleukin (IL)-3 in orchestrating anti-tumor immunity through CTL modulation. Intratumoral CTLs undergo a progressive decline in IL-3 production, which is correlated with impaired cytotoxic function. Augmenting IL-3, through intraperitoneal administration, IL-3-expressing melanoma cells, or IL-3-engineered CD8+ T cells, confers protection against tumor progression, concomitant with increased CTL activity. CTLs are critical in this therapeutic efficacy as IL-3 demonstrates no impact on tumor growth in RAG1 knockout mice or following CD8+ T cell-depletion. Rather than acting directly, CTL-derived IL-3 exerts its influence on basophils, synergistically amplifying anti-tumor immunity within CTLs. Introducing IL-3-activated basophils retards tumor progression, whereas basophil depletion diminishes the effectiveness of IL-3 supplementation. Furthermore, IL-3 prompts basophils to produce IL-4, which subsequently elevates IFN-γ production and viability of CTLs. Notably, the importance of basophil-derived IL-4 is evident from the absent benefits in IL-3-supplementated, IL-4 knockout tumor-bearing mice. Overall, this research unveils IL-3-mediated CTL-basophil crosstalk in regulating anti-tumor immunity and offers the prospect of harnessing IL-3 sustenance as a promising approach for optimizing and enhancing cancer immunotherapy.