Phosphoinositide 3-kinase delta (PI3Kd) inhibitors are used to treat lymphomas but safety concerns and limited target selectivity curbed their clinical usefulness. PI3Kd inhibition in solid tumors has recently emerged as a potential novel anti-cancer therapy through the modulation of T cell responses and direct anti-tumor activity. Here we report the exploration of IOA-244/MSC2360844, a first-in-class non-ATP-competitive PI3Kd inhibitor, for the treatment of solid tumors. We confirm IOA-244’s selectivity as tested against a large set of kinases, enzymes, and receptors. IOA-244 inhibits the in vitro growth of lymphoma cells and its activity correlates with the expression levels of PIK3CD, suggesting cancer cell-intrinsic effects of IOA-244. Importantly, IOA-244 inhibits Treg proliferation while having limited anti-proliferative effects on conventional CD4+ T cells and no effect on CD8+ T cells. Instead, treatment of CD8 T cells with IOA-244 during activation, favors the differentiation of memory-like, long-lived CD8, known to have increased antitumor capacity. These data highlight immune-modulatory properties that can be exploited in solid tumors. In CT26 colorectal and LLC lung cancer models, IOA-244 sensitized the tumors to anti-PD-1 (Programmed cell death protein 1) treatment, with similar activity in the Pan-02 pancreatic and A20 lymphoma syngeneic mouse models. IOA-244 reshaped the balance of tumor-infiltrating cells, favoring infiltration of CD8 and NK cells, while decreasing suppressive immune cells. IOA-244 presented no detectable safety concerns in animal studies and is currently in clinical Phase Ib/II investigation in solid and hematological tumors.