Mammalian cells use cytosolic nucleic acid receptors to detect pathogens and other stress signals. In innate immune cells the presence of cytosolic DNA is sensed by the cGAS–STING signalling pathway, which initiates a gene expression programme linked to cellular activation and cytokine production. Whether the outcome of the STING response varies between distinct cell types remains largely unknown. Here we show that T cells exhibit an intensified STING response, which leads to the expression of a distinct set of genes and results in the induction of apoptosis. Of note, this proapoptotic STING response is still functional in cancerous T cells and delivery of small molecule STING agonists prevents in vivo growth of T-cell-derived tumours independent of its adjuvant activity. Our results demonstrate how the magnitude of STING signalling can shape distinct effector responses, which may permit for cell type-adjusted behaviours towards endogenous or exogenous insults.