Immunotherapy, including immune checkpoint inhibitors, has revolutionized cancer treatment, but only a minor fraction of patients shows durable responses. A new approach to overcome this limitation is yet to be identified. Recently, we have shown that photobiomodulation (PBM) with near‐infrared (NIR) light in the NIR‐II window reduces oxidative stress and supports the proliferation of CD8+ T cells, suggesting that PBM with NIR‐II light could augment anti‐cancer immunity. Here, we report a novel approach to support tumor‐infiltrating CD8+ T cells upon PBM with NIR‐II laser with high tissue penetration depth. Brief treatments of a murine model of breast cancer with dual 1064 and 1270 nm lasers reduced the expression of the programmed cell death protein 1 (PD‐1) in CD8+ T cells in a syngeneic mouse model of breast cancer. The direct effect of the NIR‐II laser treatment on T cells was confirmed by the enhanced tumor growth delay by the adoptive transfer of laser‐treated CD8+ T cells ex vivo against a model tumor antigen. We further demonstrated that specific NIR‐II laser parameters augmented the effect of the immune checkpoint inhibitor on tumor growth. PBM with NIR‐II light augments the efficacy of cancer immunotherapy by supporting CD8+ T cells. Unlike the current immunotherapy with risks of undesirable drug–drug interactions and severe adverse events, the laser is safe and low‐cost. It can be broadly combined with other therapy without modification to achieve clinical significance. In addition, our study established a path to develop a novel laser‐based therapy to treat cancer effectively. [ABSTRACT FROM AUTHOR]