Antigen receptor signaling pathways that control lymphocyte activation depend on signaling hubs and negative regulatory proteins to fine-tune signaling outputs to ensure host defense and avoid pathogenic responses. Caspase recruitment domain-containing protein 11 (CARD11) is a critical signaling scaffold that translates T cell receptor (TCR) triggering into the activation of nuclear factor κB (NF-κB), c-Jun N-terminal kinase (JNK), mechanistic target of rapamycin (mTOR), and Akt. Here, we identify glutamine-rich protein 1 (QRICH1) as a regulator of CARD11 signaling that mediates an intracellular checkpoint for CD8